webadmin: truncated text in Storage-Disks sub-tab

Fixed truncated headers in Storage -> Disks sub-tab.

Change-Id: I4adca437d72c8abb75f47a15bb14536d3b5d2c4d
Bug-Url: https://bugzilla.redhat.com/922731
Signed-off-by: Daniel Erez <derez@redhat.com>