Added a test that checks throwing a NotAvailableError when adding a un-available node to a group

This is passing
Added a test that checks duplicate nic names

Test passed.
When add two nic of same name to a node, a DuplicateError is raised
Merge remote-tracking branch 'origin/devel' into unit-tests
fixed issues pointed out by zenhack
blank line between summary and docstring
Merge pull request #24 from CCI-MOC/unit-tests

Added a test that checks throwing a NotAvailableError when adding a un-a...