res_sorcery_memory_cache: Reduce cache lock time for sorcery memory cache populate...

res_sorcery_memory_cache: Reduce cache lock time for sorcery memory cache populate command

Reduce cache lock time for AMI and CLI sorcery memory cache populate
commands by adding a new populate_lock to the sorcery_memory_cache
struct which is locked separately from the existing cache lock so that
the cache lock can be maintained for a reduced time, locking only when
the cache objects are removed and re-populated.

Resolves: #1700

UserNote: The AMI command sorcery memory cache populate will now
return an error if there is an internal error performing the populate.
The CLI command will display an error in this case as well.