Ensure that crontabs package is installed

Keystone container do not have crontabs package installed which
breaks 'cron' usage in puppet manifests.

Change-Id: Id4d9258d149acd046bb7c4c4002c766dae9e3c29
Closes-Bug: #1386098
(cherry picked from commit 13d6b14810f6cff5ac729c494f39b28a5d2c3176)
Merge "Ensure that crontabs package is installed" into stable/5.1