Fix Neutron enabled check

* Remove the check for neutron enabled on a block of variable settings, there
  is no conflict and serves no purpose.
* Also floating_ips.sh and volume.sh needed to properly source lib/neutron
  for do ping_check() to work properly.

The current error in check-devstack-dsvm-neutron is not related to this fix.

Change-Id: I1c458aaa787ffb98c945aefc3afa80c6861a405f
make service_check fatal

if we fail service check, we should do so in a fatal way, because
something is not right. This will be very useful in grenade.

Change-Id: I18811b0d8e6d06f364685c366cdc8f5dda3b8f7e
Merge "Fix Neutron enabled check"
Merge "make service_check fatal"