[services] Tunnelbroker - Distinguish logging levels in dev-mode

Summary:
Distinguish glog logging levels in production (default) and dev-mode.
For the production-mode we are using the minimal logging level 2 which corresponds to ERROR and FATAL messages.
For the dev-mode we're using the minimal logging level 0 which corresponds to showing all messages including INFO and WARNING.

Linear task: ENG-1102

Test Plan:
Running yarn run-tunnelbroker-service prints only LOG(ERROR) and LOG(FATAL) messages.
Running yarn run-tunnelbroker-service-dev-mode prints LOG(INFO), LOG(WARNING), LOG(ERROR) and LOG(FATAL) messages.

Reviewers: karol-bisztyga, palys-swm

Reviewed By: karol-bisztyga, palys-swm

Subscribers: ashoat, palys-swm, Adrian, atul, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D4132