mon: QuorumService: return health status on get_health()

This allows us to return the appropriate overall health status on
Monitor::get_health().

Fixes: 4574

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
mon: Monitor: fix timechecks get_health clobbering overall status

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>