overlay/020: make sure the system supports the required namespaces

Don't run this test if the kernel doesn't support namespaces.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/overlay/020

@@ -32,10 +32,16 @@ rm -f $seqres.full
 
 # real QA test starts here
 
+require_unshare() {
+	unshare -f -r "$@" true &>/dev/null || \
+		_notrun "unshare $@: not supported"
+}
+
 # Modify as appropriate.
 _supported_fs overlay
 _supported_os Linux
 _require_scratch
+require_unshare -m -p -U
 
 # Remove all files from previous tests
 _scratch_mkfs