Replace direct error handling with 'ksft_test_result_*'
macros for better reporting.

Test logs:

Before change:
- Without root
 error: unshare, errno 1

- With root
 No, output

After change:
- Without root
TAP version 13
1..1
ok 2 # SKIP This test needs root to run!
Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0

- With root
TAP version 13
1..1
ok 1 Test : Success
Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0

Link: https://lore.kernel.org/r/20250105085255.124929-3-cvam0000@gmail.com
Signed-off-by: Shivam Chaudhary <cvam0000@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Add 'ksft_exit_skip()', if  not run as root, with an appropriate
Warning.

Add 'ksft_print_header()' and 'ksft_set_plan()' to structure test
outputs more effectively.

Test logs:

Before Change:
- Without root
 error: unshare, errno 1

- With root
 No, output

After change:

- Without root
TAP version 13
1..1
ok 2 # SKIP This test needs root to run!
Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0

- With root
TAP version 13
1..1

Link: https://lore.kernel.org/r/20250105085255.124929-2-cvam0000@gmail.com
Signed-off-by: Shivam Chaudhary <cvam0000@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Mount tmpfs with "nr_inodes=3" for easy check.

Link: http://lkml.kernel.org/r/20190219215016.GA20084@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matej Kupljen <matej.kupljen@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>