Define global logger instance to be used for all logging

Summary:
The advantage of this is that anyone can now log without needing to carry around a Logger object.
Primary reason is for making metrics less intrusive in the codebase.

Reviewed By: passy

Differential Revision: D13671368

fbshipit-source-id: 162ab1351a124683aef13983fc3bcec01385cd1a

src/server.js

@@ -185,7 +185,6 @@ export default class Server extends EventEmitter {
                 destination,
               ),
               'processCertificateSigningRequest',
-              this.logger,
             )
               .then(result => {
                 subscriber.onComplete({