frontend: console native execution in iframes

currently when user runs a console using 'native' invocation, the
request is made in a new tab. this patch changes the behavior and opens
requests in iframes instead. this is more convenient as the execution
doesn't open a new tab for every vm involved.

Change-Id: I042213dd16fdab94b431ea0564a3780b79234e69
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1052077