Remove Lock/Unlock methods from imageStore
Remove Lock/Unlock methods from imageStore

They are now only used in the constructors, so use a variant
of startReading/startWriting instead.  This code path is not
performance-critical, so let's share as much code as possible
to ensure consistency in locking.

Should not change behavior.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

containers/storage,containers/storage,containers/storage