ipatests: allocate pseudo-terminal only for specific command
While "ktutil" does require a pseudo-terminal on particular systems to
operate, majority of programs do not need it.
At the same time invoking `ssh` with forced pseudo-terminal allocation
interferes with sessions multiplexing feature and increases connection
time. The increase can be as large as 10 seconds in certain cases which
leads to unexpected EOFs of pexpect utility.
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>