Only read storage.conf once
Only read storage.conf once

Currently running a simple container runs and stats configuration
storage.conf files multiple times on a simple container run.

This PR cuts the opens and stats in half by caching the first read.
This speeds up start by about 10-20 microseconds.

If container engines want to react to storage files changing, added a
new function UpdateStoreOptions to allow engines to reload options.

Fixes: https://github.com/containers/storage/issues/1403

Signed-off-by: Daniel J Walsh <7800de746fd39599bc46177380ea6aede7e31e16@redhat.com>

containers/storage,containers/storage,containers/storage