Converts cron-apt tests Serverspec -> TestInfra
Converts cron-apt tests Serverspec -> TestInfra

Ran into a bit of trouble with the Firefox version pinned as part of the
Selenium config, since that broke checks for "all upgrades have been
installed." Added a logic branch in the tests that permits Firefox
if it's the only package listed in the list of upgradeables.

micahflee/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,micahflee/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,ageis/securedrop,ageis/securedrop,ageis/securedrop,micahflee/securedrop,heartsucker/securedrop,conorsch/securedrop,garrettr/securedrop,heartsucker/securedrop,ageis/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,garrettr/securedrop,garrettr/securedrop,garrettr/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,micahflee/securedrop