testimage: use the new targetcontrol.py module for running tests

testimage: use the new targetcontrol.py module for running tests

This patch makes the necessary changes for using the targetcontrol.py module
so that one can run the same tests on a qemu instance or a remote machine
based on the value of TEST_TARGET variable: "qemu" or "simpleremote".
The default value is "qemu" which starts a qemu instance and it's the
with what we currently have.

With "simpleremote", the remote machine must be up with network and ssh
and you need to set TEST_TARGET_IP with the IP address of the remote machine
(it can still be a qemu instance that was manually started).

Basically testimage.bbclass now does something along the lines of:
 - load tests -> deploy (prepare) / start target -> run tests.
There were a couple of changes necessary for tests and
also some cleanups/renames that were needed to adjust this change. (use
ip everywhere when refering to target and server_ip when refering to host/build machine)
Also two unnecessary and unsed methods were dropped from sshcontrol.

[ YOCTO #5554 ]

(From OE-Core rev: a7820350fa3271d78ed7476e02f4aef593be1125)

Signed-off-by: Stefan Stanacar <stefanx.stanacar@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>