makefs: tests: Fix timestamp-related tests

[jlduran]

Summary

Use a variable for mtree that includes the DEFAULT_MTREE_KEYWORDS, in
order to avoid missing the important "time" keyword.

Unskip the "failing" tests, and comment out the specific failing checks,
these will be addressed (or at least discussed) in a different revision.

For MS-DOS tests, use an even value timestamp, as precision is 2s.

For ZFS tests, use import_image instead of mount_image consistently.

[markj]

usr.sbin/makefs/tests/makefs_zfs_tests.sh

978

These options are all redundant, i.e., atf_check will verify them by default. Generally I omit them on purpose to make test code a bit neater. But I guess it's better to be consistent with other tests of the same type.

[bnovkov]

usr.sbin/makefs/tests/makefs_cd9660_tests.sh

40

I would consider moving the MTREE variable definition to makefs_tests_common.sh since all its contents are the same in all three scripts, but I won't insist.

[jlduran]

usr.sbin/makefs/tests/makefs_cd9660_tests.sh

40

Yes! It will be addressed upon commit.

usr.sbin/makefs/tests/makefs_zfs_tests.sh

978

I agree, and I'll try to address this suggestion in D54427; however, there is a high probability it may not be accepted.