Configuration to disable gRPC native logging

[pedelman]

When running a gRPC server with Gruf I notice logs such as:

deadline is 1969-12-31 23:59:59 +0000; (now=2017-05-04 21:56:58 +0000)

or

schedule another job

When investigating, I see that the logs are coming from the gRPC logger. (https://github.com/grpc/grpc/blob/6ff81e91c9577a52252460fb029fbbf990cfc7b6/src/ruby/lib/grpc/generic/rpc_server.rb#L80)

It would be nice to support a configuration option to disable this kind of logging from configuration in Gruf.

[splittingred]

Solved in #13