Hold puppetmaster version to 2.7.11-1ubuntu2.3

There seems to be a bug in 2.7.11-1ubuntu2.4 that causes staffords CPU
to spike. While we chase down the bug with Ubuntu/upstream hold the
version of puppet packages on puppetmaster's

Change-Id: I9452dba4d525b93ee229f5bfb3c99513417195c7