Add Charm Relations Tests and Tags

This commit adds Robot Tests for the following
cases:

Basic 13 NS Relations
Basic 14 VNF Relations

It also adds tags to charm tests so that they can
be executed by themselves and the charm tag to
execute all charm related tests.

Change-Id: I2ee5780a8a832c3535d1739b3effa4b57b880be2
Signed-off-by: Dominik Fleischmann <dominik.fleischmann@canonical.com>