Make logging configurable about cloud-sql-proxy

[olivierboucher]

@Carrotman42 Can you tell me if the current interface suits you? I'm pretty sure it would be compatible with most logging libraries. Just give me a clear and I'll replace references to the stdlib logger in the entire repo

[Carrotman42]

Sure, that makes a lot of sense.

But please note: you really /should/ be pooling connections. Particularly with the proxy, dialing new database connections is significantly less efficient than using existing connections.

[olivierboucher]

I could submit a pull request if you can tell me which logging library you would like to use.

[Carrotman42]

As for what library to use, I would prefer to continue using the standard logging library in Go. But, it'd be best to abstract it so that users of the Go library can swap in their own favorite logging library if they feel like it. My initial thought is to create a new package ` github.com/GoogleCloudPlatform/cloudsql-proxy/log` which contains exported variables `Infof`, `Verbosef`, etc which simply forward to the stdlib's `log.Infof`. In the main file, a "--verbose" flag should be defined, and an init function should overwrite the definition of `log.Verbosef` to first check the flag value and then drop the log if the flag is false.

[olivierboucher]

Thanks, will submit a PR soon

[Carrotman42]

@olivierboucher sorry I didn't see your comment from a day ago, and I'm also not exactly sure which interface you mean.

After receiving #100 I went ahead and made the changes I suggested in #44 (comment). This will be sent out later today.

[Carrotman42]

Setting -verbose=false will now turn off the new/closed connection logs. Note that errors which are not EOF will still be logged when in non-verbose mode since these may be useful for debugging client-/server-side problems. Those who would like to disable all output can use the -quiet flag submitted in #100