Bug 1939 fixed: : added a random suffix to the end of the Juju app name, in order...

I followed the second option of the bug's description. Now, Juju
applications have a random suffix with size=5 (the random suffix
size used by K8s), in order to avoid collisions between applications'
names;

Also fixed unit-test on test_n2vc_juju_conn.py

Change-Id: I5d3eb8282889e58361f7c21214b11071a7530d26
Signed-off-by: Pedro Escaleira <escaleira@av.it.pt>