ComputeFilter shouldn't generate a warning for disabled hosts

Disabling a service is a normal operation, so this state should
not be included in the same log statement as a host that fails
the service_is_up() check.

A service which is enabled but not up deserved a warning rather
than debug entry.

By separating out the checks we also avoid the service check on
disabled hosts.

Change-Id: I1a398bc033ebe71f42ac117af7dae39502aceede
Closes-Bug: 1254356
Merge "ComputeFilter shouldn't generate a warning for disabled hosts"