host manager: Log the host generating the warning

Currently we are logging a warning when there's a discrepancy between
the host's available disk stored in the database and the disk reported
by the compute node, but there's no information about which host
generates that error.

Change-Id: I8d6704fa76f2750e0e986b8399f9fe358b3fad93
Merge "host manager: Log the host generating the warning"