Job control in emergency shell

Job control was not working in the rescue shell.  Replace the
call to bash with openvt, which fulfills all of bash's internal
requirements to enable job control.

rhbz#753315

Change-Id: Idcb0ef9053d43b26645c6e4c6dcc6108a1e7916c
Signed-off-by: Ryan Barry <rbarry@redhat.com>