Make travis use Makefile when running tests

Do not hard-code `python -m unittest` or `nosetests` statements into the travis
config file. Instead, place those statements in the primary Makefile and make
Travis call the recipes in the Makefile.

Rename recipe "test" to "test-robottelo", which more accurately reflects its
purpose.
Merge pull request #908 from Ichimonji10/travis

Make travis use Makefile when running tests