build: Add -c and --cmd as aliases for --task

This aligns us with bitbake. Moreover, -c/--cmd is easier to tell apart
from --target. Keep --task for backward compatibility.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas-docker

@@ -147,7 +147,7 @@ while [ $# -gt 0 ]; do
 		trace docker run ${DOCKER_IMAGE} ${CMD} --help
 		exit 0
 		;;
-	--skip|--target|--task|-c|--command)
+	--skip|--target|--task|-c|--cmd|--command)
 		KAS_OPTIONS="${KAS_OPTIONS} $1 '$2'"
 		shift 2
 		;;