webadmin: wrong memory overcommit unit

in cluster general info sub tab, Max Memory Over Commitment
unit is MB, and should be %

Change-Id: Ie572092251bc5d5a87f9734f18194389cf1fbe29
Bug-Url: https://bugzilla.redhat.com/1021326
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>