Move Login#token before/each within context

So that the munging of ENV, Fog.credential and Fog.credentials_path is
isolated to the context that's using it. In preperation for moving the other
Login#token tests back into this same file.
Reinstate Login#token integration tests

This reverts commit ad15254 which moved these to a file that wouldn't be
picked up by rspec's glob. They have been modified so as not to conflict
with what we discovered in 09ef65f and e766457.

We're able to run these in CI because we still have access to the original
password injected by Jenkins which is used by `vcloud-login` in
`jenkins_tests.sh`. When not run in CI and the environment variable isn't
set, these tests will be marked as pending.
Merge pull request #116 from gds-operations/reinstate_fog_login_test

Reinstate Login#token integration tests