test_runtime.sh: Add a user namespace

You shouldn't need to be root to test a runtime.  The id calls use the
POSIX command [1] to find the current user's user and group IDs.

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/id.html

Signed-off-by: W. Trevor King <wking@tremily.us>

test_runtime.sh

@@ -78,7 +78,7 @@ tar -xf  rootfs.tar.gz -C ${TESTDIR}
 cp runtimetest ${TESTDIR}
 
 pushd $TESTDIR > /dev/null
-ocitools generate "${TEST_ARGS[@]}" --rootfs '.'
+ocitools generate "${TEST_ARGS[@]}" --rootfs '.' --user '' --uidmappings "$(id -u):0:1" --gidmappings "$(id -g):0:1"
 popd > /dev/null
 
 TESTCMD="${RUNTIME} start $(uuidgen)"