webadmin: Japanese - truncated text in target list

Storage Domain dialog - target list:
fix 'Dev.Size' column width.

Change-Id: I569b5f86bdd00ecb1f9c78a47306a44aeb89e209
Bug-Url: https://bugzilla.redhat.com/927504
Signed-off-by: Daniel Erez <derez@redhat.com>