Fix co-existence with riemann-client under py3

[huguesb]

bernhard==0.2.6 and riemann-client==6.5.0 are incompatible under python 3.7 when the protobuf package is using the C++ implementation (as opposed to pure python). This is easily reproduced:

# python3
Python 3.7.6 (default, Dec 19 2019, 23:49:42)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from python_metrics.metric_emitter import Metric, MetricClosedError
>>> import bernhard
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/virtualenv/ml-serving/lib/python3.7/site-packages/bernhard/__init__.py", line 18, in <module>
    from . import proto_pb2 as pb
  File "/opt/virtualenv/ml-serving/lib/python3.7/site-packages/bernhard/proto_pb2.py", line 22, in <module>
    serialized_pb=_b('\n\x0bproto.proto\"\x81\x01\n\x05State\x12\x0c\n\x04time\x18\x01 \x01(\x03\x12\r\n\x05state\x18\x02 \x01(\t\x12\x0f\n\x07service\x18\x03 \x01(\t\x12\x0c\n\x04host\x18\x04 \x01(\t\x12\x13\n\x0b\x64\x65scription\x18\x05 \x01(\t\x12\x0c\n\x04once\x18\x06 \x01(\x08\x12\x0c\n\x04tags\x18\x07 \x03(\t\x12\x0b\n\x03ttl\x18\x08 \x01(\x02\"\xce\x01\n\x05\x45vent\x12\x0c\n\x04time\x18\x01 \x01(\x03\x12\r\n\x05state\x18\x02 \x01(\t\x12\x0f\n\x07service\x18\x03 \x01(\t\x12\x0c\n\x04host\x18\x04 \x01(\t\x12\x13\n\x0b\x64\x65scription\x18\x05 \x01(\t\x12\x0c\n\x04tags\x18\x07 \x03(\t\x12\x0b\n\x03ttl\x18\x08 \x01(\x02\x12\x1e\n\nattributes\x18\t \x03(\x0b\x32\n.Attribute\x12\x15\n\rmetric_sint64\x18\r \x01(\x12\x12\x10\n\x08metric_d\x18\x0e \x01(\x01\x12\x10\n\x08metric_f\x18\x0f \x01(\x02\"\x17\n\x05Query\x12\x0e\n\x06string\x18\x01 \x01(\t\"g\n\x03Msg\x12\n\n\x02ok\x18\x02 \x01(\x08\x12\r\n\x05\x65rror\x18\x03 \x01(\t\x12\x16\n\x06states\x18\x04 \x03(\x0b\x32\x06.State\x12\x15\n\x05query\x18\x05 \x01(\x0b\x32\x06.Query\x12\x16\n\x06\x65vents\x18\x06 \x03(\x0b\x32\x06.Event\"\'\n\tAttribute\x12\x0b\n\x03key\x18\x01 \x02(\t\x12\r\n\x05value\x18\x02 \x01(\tB\x1a\n\x11\x63om.aphyr.riemannB\x05Proto')
  File "/opt/virtualenv/ml-serving/lib/python3.7/site-packages/google/protobuf/descriptor.py", line 884, in __new__
    return _message.default_pool.AddSerializedFile(serialized_pb)
TypeError: Couldn't build proto file into descriptor pool!
Invalid proto descriptor for file "proto.proto":
  State.time: "State.time" is already defined in file "riemann.proto".
  State.state: "State.state" is already defined in file "riemann.proto".
  State.service: "State.service" is already defined in file "riemann.proto".
  State.host: "State.host" is already defined in file "riemann.proto".
  State.description: "State.description" is already defined in file "riemann.proto".
  State.once: "State.once" is already defined in file "riemann.proto".
  State.tags: "State.tags" is already defined in file "riemann.proto".
  State.ttl: "State.ttl" is already defined in file "riemann.proto".
  State: "State" is already defined in file "riemann.proto".
  Event.time: "Event.time" is already defined in file "riemann.proto".
  Event.state: "Event.state" is already defined in file "riemann.proto".
  Event.service: "Event.service" is already defined in file "riemann.proto".
  Event.host: "Event.host" is already defined in file "riemann.proto".
  Event.description: "Event.description" is already defined in file "riemann.proto".
  Event.tags: "Event.tags" is already defined in file "riemann.proto".
  Event.ttl: "Event.ttl" is already defined in file "riemann.proto".
  Event.attributes: "Event.attributes" is already defined in file "riemann.proto".
  Event.metric_sint64: "Event.metric_sint64" is already defined in file "riemann.proto".
  Event.metric_d: "Event.metric_d" is already defined in file "riemann.proto".
  Event.metric_f: "Event.metric_f" is already defined in file "riemann.proto".
  Event: "Event" is already defined in file "riemann.proto".
  Query.string: "Query.string" is already defined in file "riemann.proto".
  Query: "Query" is already defined in file "riemann.proto".
  Msg.ok: "Msg.ok" is already defined in file "riemann.proto".
  Msg.error: "Msg.error" is already defined in file "riemann.proto".
  Msg.states: "Msg.states" is already defined in file "riemann.proto".
  Msg.query: "Msg.query" is already defined in file "riemann.proto".
  Msg.events: "Msg.events" is already defined in file "riemann.proto".
  Msg: "Msg" is already defined in file "riemann.proto".
  Attribute.key: "Attribute.key" is already defined in file "riemann.proto".
  Attribute.value: "Attribute.value" is already defined in file "riemann.proto".
  Attribute: "Attribute" is already defined in file "riemann.proto".
  Event.attributes: "Attribute" seems to be defined in "riemann.proto", which is not imported by "proto.proto".  To use it here, please add the necessary import.
  Msg.states: "State" seems to be defined in "riemann.proto", which is not imported by "proto.proto".  To use it here, please add the necessary import.
  Msg.query: "Query" seems to be defined in "riemann.proto", which is not imported by "proto.proto".  To use it here, please add the necessary import.
  Msg.events: "Event" seems to be defined in "riemann.proto", which is not imported by "proto.proto".  To use it here, please add the necessary import.

Updating bernhard's proto.proto to use a package stanza, and re-running protoc solves this issue.