tests: Add a test for 1 master, 1 slave, 1 observer, no connections
tests: Add a test for 1 master, 1 slave, 1 observer, no connections

The case worked already just fine, but adding a unit test to keep
it from regressing.

saaros/pglookout,Ormod/pglookout,Ormod/pglookout,ohmu/pglookout