Make shotgun to work inside containers

Previously, the config is generated with assumption that master/postgres
node is localhost. Since now, the addresses are getting from external
settings file (/etc/nailgun/settings.yaml).

Closes-Bug: 1312620
Closes-Bug: 1313839

Change-Id: If041cae5b06fb12e1085107147f75922a066ae37
Merge "Make shotgun to work inside containers"