Add tests for 3 syscalls in "file-close" audit class

[aniketp_iitk.ac.in]

Summary

The following changes introduce a new test-program file-close , which introduces tests for the
following 3 system calls in both success and failure mode

• munmap(2)
• close(2)
• revoke(2)

Note: These are the only system calls in "fc" audit class

Test Plan

Execute make && make install from test/sys/audit.
Execute kyua test from /usr/tests/sys/audit. All testcases should succeed.