Inconsistent configuration default for `experimental` features

[valentin-seitz]

Extrae has some features it deems experimental
As of version, v4.2.1 they are:

• instrument-io Default: ENABLED
• instrument-dynamic-memory Default: ENABLED
• instrument-syscall Default: ENABLED
• bfd-generate-addresses Default: ENABLED, because depended on instrument-dynamic-memory
• dcarrera-hadoop Default: DISABLED

As #51 pointed out, it might be a better default to disable experimental features by default?