Hypervisor uptime fails if service is disabled

Getting the uptime of a hypervisor fails because the db query
used to get the service filters out disabled hosts.

Instead we replace that query with one that always gets the
service if it exists, and a check that the sevice is up to
avoid an rpc call to a non running service.

Fixes bug 1195052

Change-Id: I97bc8a5002bd0f333207403d5b1878649612b762
Merge "Hypervisor uptime fails if service is disabled"