Remove system_metadata db calls from compute manager

The compute/manager makes several unnecessary db calls to fetch
the instance system_metadata, which is available in the instance
object itself now. This patch replaces those uses, avoiding the
need to farm them out to conductor.

Related to bp/no-db-compute
Related to bp/no-db-compute-manager

Change-Id: I26ff77be17eb538a4fcd238ffe52f8bde4fbe3e0
Sync timeutils changes from Oslo

Change-Id: I5eddfbad43a2f57e6b2af6299e480c32b11a5d19
Merge "Remove system_metadata db calls from compute manager"
Merge "Sync timeutils changes from Oslo"