Add tests for 5 syscalls in "file-delete" audit class

[aniketp]

Summary

The following changes introduce a new test-program file-delete, apart from the already existing 24 tests for fc "file-create" audit class which were introduced in D15286 and committed as rS334360 and 8 more such tests. These 10 test cases check the proper audit of folllowing system calls

• rmdir(2)
• unlink(2)
• unlinkat(2)
• rename(2)
• renameat(2)

Note: open(2) and openat(2) will be handled in a separate test-program.

Test Plan

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

[asomers]

These test programs need to be marked as is_exclusive (as do all of the other audit tests).

[aniketp]

Add a test-case metadata to ensure that the tests don't run in parallel:
TEST_METADATA+= is_exclusive="true"