Add tests for truncate(2) and ftruncate(2) system calls

[aniketp]

Summary

Following the pattern of D15636:

The following changes introduce a new test-program file-write, apart from the already existing 28 tests for fcfile-creat andfile-read audit class which were introduced in D15286 & D15636 and committed as rS334360 & rS334471. These 4 test-cases check the proper audit of truncate(2) and ftruncate(2) for both success and failure case.

Test Plan

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

[asomers]

Is this the entire fw audit class?

[aniketp]

Yes, apart from open and openat, truncate and ftruncate are the only syscalls in this class