webadmin: Japanese - truncated text in snapshots sub-tab

VMs - snapshots sub-tab:
- fix columns width.
- change header cells 'white-space' to normal
  (to allow multiple rows).

Change-Id: I02f7afb0b7521886df2cf0d99fa9d2b19e077d31
Bug-Url: https://bugzilla.redhat.com/927617
Bug-Url: https://bugzilla.redhat.com/951067
Bug-Url: https://bugzilla.redhat.com/950289
Signed-off-by: Daniel Erez <derez@redhat.com>