Autotest module for testing crontab

The module tests the functionality of crontab of the system.
Crontab depends upon the binary run-parts, which is used to run
all scripts under a directory.An entry in the crontab is added
by creating an entry in /etc/crontab.

The module uses the run-parts to execute a script(named cron) created under
/etc/cron.d/ and the script is made to execute every 60 seconds.The script
writes a certain string to a file(/tmp/autotest_cron-<date>).The count of
the string after t seconds decides whether the test succeeded
or not.

The two files used along with run-parts for selective execution of
scripts (jobs.allow and jobs.deny) are also covered under the test.
jobs.allow specifies the scripts to be run and deny specifies scripts
to be ignored.These conditions are also checked.

Signed-off-by: Rajeev S <rajeevs1992@gmail.com>