Add parameters to test_upgrade_vpc.py to all overrides
Add parameters to test_upgrade_vpc.py to all overrides

Two new environment variables have been added that allow providing a path to a config.yaml that defines override properties for the install of the cluster and the upgrade of the cluster.

* CONFIG_YAML_OVERRIDE_INSTALL
* CONFIG_YAML_OVERRIDE_UPGRADE

BenWhitehead/dcos,amitaekbote/dcos,mesosphere-mergebot/mergebot-test-dcos,jeid64/dcos,mesosphere-mergebot/dcos,darkonie/dcos,mellenburg/dcos,amitaekbote/dcos,lingmann/dcos,BenWhitehead/dcos,kensipe/dcos,dcos/dcos,BenWhitehead/dcos,surdy/dcos,mnaboka/dcos,lingmann/dcos,mellenburg/dcos,branden/dcos,vishnu2kmohan/dcos,amitaekbote/dcos,vishnu2kmohan/dcos,darkonie/dcos,mesosphere-mergebot/dcos,mesosphere-mergebot/mergebot-test-dcos,GoelDeepak/dcos,surdy/dcos,lingmann/dcos,GoelDeepak/dcos,mnaboka/dcos,branden/dcos,vishnu2kmohan/dcos,amitaekbote/dcos,vishnu2kmohan/dcos,darkonie/dcos,surdy/dcos,mesosphere-mergebot/mergebot-test-dcos,mesosphere-mergebot/dcos,branden/dcos,mellenburg/dcos,dcos/dcos,mnaboka/dcos,asridharan/dcos,darkonie/dcos,dcos/dcos,asridharan/dcos,jeid64/dcos,branden/dcos,kensipe/dcos,mellenburg/dcos,mesosphere-mergebot/mergebot-test-dcos,lingmann/dcos,asridharan/dcos,GoelDeepak/dcos,kensipe/dcos,mesosphere-mergebot/dcos,jeid64/dcos,mnaboka/dcos,jeid64/dcos,GoelDeepak/dcos,asridharan/dcos,dcos/dcos,BenWhitehead/dcos,surdy/dcos,darkonie/dcos,mnaboka/dcos,dcos/dcos,kensipe/dcos