Previously only plugin.sh was validated.
At the monent some parts of the plugin
were moved under devstack/lib to increase plugin.sh
readability. Those files were not validated.
Note:
Tweaked a tox.ini by removing installing the monasca-api
package in environments that do not actually need it.
Also removed redundant references to main environment
dependencies.
Change-Id: I43381647228fad99603b5717c37496e80f409d4f