webadmin: spiceProxyOverrideEnabled label overlapped in spanish

Fixed by setting the label big enough so the translated text fits in

Change-Id: I1e02bd278e79d2571eb99b7dab70bab1c775bc81
Bug-Url: https://bugzilla.redhat.com/1088868
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>