Add Quiet Flag

[mykolasmith]

Hello,

This pull requests adds a -quiet flag. I am using cloud_sql_proxy in production on Google Container Engine, per these instructions, and the constant "Connection established" logging pollutes our log streams (and will eventually incur additional costs to Stackdriver Logging). Please consider merging this PR so that we may silence logging.

Thanks!

[mykolasmith]

Partially addresses #44

[Carrotman42]

Hmm, I'm OK to accept this pull request because it addresses real problems people have raised, but this will basically make debugging any sort of errors impossible. Thus, my only request is add a single log line before turning off the output which says something along the lines of:

"WARNING: the -quiet flag has disabled all output; errors from connections will not be printed out which will likely make debugging difficult"

[mykolasmith]

Added via https://github.com/GoogleCloudPlatform/cloudsql-proxy/pull/100/files#diff-7f281af6c5a5fdeaf6d11de9ee145a2dR343

[Carrotman42]

I appreciate the pull request!

[mykolasmith]

@Carrotman42 when can we expect a v1.10 release w/ these changes?

[Carrotman42]

I will release a new version either tomorrow or next Monday (June 26). Thank you for your patience.

[Carrotman42]

The new docker image is available at gcr.io/cloudsql-docker/gce-proxy:1.10, but unfortunately the internal site that we use to release the precompiled binary at https://dl.google.com/cloudsql/cloud_sql_proxy.linux.amd64 is down. Apologies for the delay, but once the internal site is back up I'll do an official release on this github site.

[Carrotman42]

Released! https://github.com/GoogleCloudPlatform/cloudsql-proxy/releases/tag/1.10