rgw/d4n: squashing following commits that add support for

rgw/d4n: squashing following commits that add support for
WATCH, EXEC, INCR, MULTI and DISCARD redis commands.

1. d4n/directory: support for watch, exec and incr methods in Block
and Object Directory.
2. d4n/directory: support for redis MULTI and DISCARD command,
adding a test case to exercise usage of MULTI.

Co-authored-by: Samarah <samarah.uriarte@ibm.com>
Adjusted log levels for directory methods added in this commit.

Signed-off-by: Pritha Srivastava <prsrivas@redhat.com>