webadmin: wrong compatibility version prompt in new DC

In case a DC was selected in grid and new DC button was pressed, we
opened the compatibility version changed dialog wrongfuly.

Added isNew DC check.

Change-Id: I85fbabe1117c64896772a52f533868d3c4a349b2
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>