(#9440) Allow cron vars to have leading whitespace

Patch applied from Jeremy Thornhill. This allows whitespace to appear before
cron variables. Previously, whitespace before cron variables would trigger a
parse failure, and the crontab, except for the puppet managed portion, would
get removed. This addresses that issue. It also includes a test for this issue,
added into the tests directory, which seems to be where the crontab tests live.

Signed-off-by: Matthaus Litteken <matthaus@puppetlabs.com>