After #5532 (e745436df3), it was no longer
possible to enable ansible colorized output. Even though
`ANSIBLE_NOCOLOR` has no effect *at the moment* in vagrant+ansible
integration, I agree to keep it for clarity and consistence.
The new `--no-color` behaviour (bug fix#5531) is now covered by a unit
test.
//cc @marsam, @sethvargo