Kvdb Debug Log Wrapper

[adityadani]

• Add a new kvdb option: DebugLogFileNameKey
• If the above option is specified it adds a wrapper over the kvdb object to log every request on the kvdb package if configured.
• In case of etcdv3 if the above option is enabled it adds a grpc interceptor to the etcd client to log every etcd request

A typical kvdb request debug log will look like this

time="2019-03-15T01:38:24-07:00" level=info caller="github.com/portworx/porx/storage/driver/volume.kvdbSpec.put" key="storage/spec/f6703b28-0f05-4f40-8584-4295d2f73be4" method="github.com/portworx/porx/vendor/github.com/portworx/kvdb.(*debugKvdb).CompareAndSet" type=etcdv3-kv
time="2019-03-15T01:38:24-07:00" level=info msg=Start method="/etcdserverpb.KV/Txn"
time="2019-03-15T01:38:24-07:00" level=info msg=Successful duration=38.945493ms method="/etcdserverpb.KV/Txn"
time="2019-03-15T01:38:24-07:00" level=info msg=Start method="/etcdserverpb.KV/Range"
time="2019-03-15T01:38:24-07:00" level=info msg=Successful duration=24.855404ms method="/etcdserverpb.KV/Range"

[codecov-io]

Codecov Report

Merging #78 into master will decrease coverage by 0.21%.
The diff coverage is 4.76%.

@@            Coverage Diff             @@
##           master      #78      +/-   ##
==========================================
- Coverage   68.53%   68.32%   -0.22%     
==========================================
  Files           7        7              
  Lines        3417     3438      +21     
==========================================
+ Hits         2342     2349       +7     
- Misses        845      860      +15     
+ Partials      230      229       -1

Impacted Files	Coverage Δ
etcd/v3/kv_etcd.go	66.23% <4.76%> (-1.12%)	⬇️
consul/kv_consul.go	73.03% <0%> (+0.58%)	⬆️

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[harsh-px]

can you change this to /var/cores since that's where we are storing all of your support bundles?

[harsh-px]

exported function. Add function comment