Trimming white spaces and adding single quotes

Trimming mac address string and adding single quotes to let user
notice other bad inputs

Change-Id: I42aaef37b882fad4e5b37f5ba859034910fc84be
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1076564
Signed-off-by: Simone Tiraboschi <stirabos@redhat.com>