neutron-ha-tool: Only treat specific exit code as failure

A router migration is only required when neutron-ha-tool exits with the exit
code '2'. All other exit codes (actually there is only '1') occur when there a
generic neutron problems (server not reachable, database offline, ...). In
these cases we should be trying to migrate router, it would fail anyway.
eutron-ha-tool less verbose logging

Call the neutron-ha-tool with --quiet in the monitor operation to not polute
syslog with useless info messages.