Change implementation of StratPool::read_metadata
Change implementation of StratPool::read_metadata

Do not sort all when only most recent metadata is of interest.
The algorithm is now just linear in the number of devices,
which ought to be faster. It has fewer lines overall, and requires
only one expect().

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

trgill/stratisd,mulkieran/stratisd,trgill/stratisd,stratis-storage/stratisd,mulkieran/stratisd,stratis-storage/stratisd,stratis-storage/stratisd