Fix quota_health_monitor opt name in neutron.conf

Reasons:
- quota_healt_monitor does not exist

Changes:
- Use quota_health_monitor instead of quota_health_monitors

Change-Id: I31d6a0394a786d26f7a063afbd3b6e07fae49b9b
fixes tests using called_once_ without assert

A few tests were using mock's called_once, or called_once_with_args
instead of assert_called_once or assert_called_once_with_args. Those
methods return a bool that needs to be actively checked.

The tests are fixed to avoid them from passing if the call condition
is not met.

Change-Id: I21e5257b26b2a08cc8f0b108233d1d5cc0b97b89
Closes-bug: #1297875
Merge "Fix quota_health_monitor opt name in neutron.conf"
Merge "fixes tests using called_once_ without assert"