CDS: Fix deleteSnapshots criteria in SnapshotManager

CDS: Fix deleteSnapshots criteria in SnapshotManager

The SnapshotManager specifies a magic number 43200000 as the timestamp
for the criteria passed to deleteSnapshots. It's unclear where this
number came from but it prevents prior snapshots from getting deleted
as stored snapshot timestamps will be greater than this value (unless
one was created back in the 70's or 80's :)). Since the SnapshotManager
passes a valid upper bounds for the criteria's maxSequenceNr, I changed
it to pass Long.MAX_VALUE for the timestamp.

The ReplicationAndSnapshotsIntegrationTest actually verifies prior
snapshots were deleted by checking for size 1 when querying the
InMemorySnapshotStore. However this only passes b/c the
InMemorySnapshotStore::doDelete is incorrect in that it doesn't compare
the stored snapshot timestamp against the criteria timestamp. So I
changed the InMemorySnapshotStore to correctly compare the timestamps as
well. I found the source for an InMemorySnapshotStore on line and that's
what it does.

Change-Id: Ie7d5eec14f684a469f4b6ff84732c9a9c6042360
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>