tests: Test aborts due to missing requirements should be marked as error instead of skipped

Many tests abort due to not being root or missing tools, for instance mkfs
commands for file system tests. The tests are exited with code 77, which
means they were skipped. A skipped test is a test that should not be run,
e.g. a test specific to ARM64 should not be run on an x86 build. These aborts
are actually a hard error, code 99. That means that the test could not be
completed, but not because what was supposed to be tested failed, e.g. in
these cases where a missing tool prevents the running of a test.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

tests/squashfs_test.in

@@ -4,7 +4,7 @@ set -e
 
 if ! which mksquashfs >/dev/null 2>&1; then
    echo "mksquashfs not installed; cannot test squashfs."
-   exit 77
+   exit 99
 fi
 
 "@builddir@/grub-fs-tester" squash4_gzip