selftest: acct: Add selftest for the acct() syscall

The acct() system call enables or disables process accounting.
If accounting is turned on, records for each terminating process
are appended to a specified filename as it terminates. An argument of NULL
causes accounting to be turned off.

This patch will add a test for the acct() syscall.

Signed-off-by: Abdulrasaq Lawani <abdulrasaqolawani@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>