webadmin: LUNs table - prevent focus on margin click

AbstractSanStorageList:
LUNs table tree leaf - use marginLeft instead of paddingLeft
to prevent focus when clicking the margin.

Change-Id: Iaca0e7a6a3600cb955add272caf5e87696ee457f
Bug-Url: https://bugzilla.redhat.com/856940
Signed-off-by: Daniel Erez <derez@redhat.com>