Achieve capacity limits

[duanhongyi]

The basic function of capacity limitation is realized. As long as the GetBucketUsage method is implemented in the backend; I only realize the backend of Minio at present, add the following parameters:

   --provider value             The specific provider of the object storage service. (default: "unknow")
   --capacity value             Limit the maximum capacity quota of mounted files. (default: 1125899906842624)
   --disk-usage-interval value  Time interval for statistics of disk usage, in seconds. (default: 60)

for example:

geesefs --provider minio \
  --capacity 629145600 \
  --disk-usage-interval 30 \
  --endpoint https://play.min.io \
  geesefs \
  /mnt/geesefs

[vitalif]

Hi, I'll review it soon, one request: can you please avoid mixing new code with formatting changes? I.e. ideally, existing code that's unchanged shouldn't be affected by the PR

[duanhongyi]

OK, I'll deal with it tomorrow.