support/testing: add python-crossbar tests

support/testing: add python-crossbar tests

This test invokes "crossbar version" command, that checks all
dependencies found in setup.py files and prints some system related
information.
Add haveged to the target to generate enough entropy so crossbar ->
pynacl -> libsodium don't hang waiting for /dev/random.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
[Ricardo: move test script to a separate file, remove Python 2 variant,
 add haveged to target to add entropy and avoid hanging]
Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>