new: check compose file yaml before usage.

bin/compose

@@ -1799,6 +1799,18 @@ export DOCKER_DATASTORE=${DOCKER_DATASTORE:-/srv/docker-datastore}
 export COMPOSE_YML_FILE=$(get_compose_yml_location) || exit 1
 debug "Found 'compose.yml' file in '$COMPOSE_YML_FILE'."
 
+output=$(shyaml get-value < "$COMPOSE_YML_FILE" 2>&1)
+if [ "$?" != 0 ]; then
+    err "Invalid YAML in '$COMPOSE_YML_FILE':"
+    while IFS='' read -r line1 && IFS='' read -r line2; do
+        echo "$line1 $GRAY($line2)$NORMAL"
+    done < <(echo "$output" | grep ^yaml.scanner -A 100 |
+                    sed -r 's/^  in "<stdin>", //g' | sed -r 's/^yaml.scanner.[a-zA-Z]+: //g') |
+        prefix "  $GRAY|$NORMAL "
+    exit 1
+fi
+
+
 if ! [ -d "$CHARM_STORE" ]; then
     err "Charm store path $YELLOW$CHARM_STORE$NORMAL does not exists. "
     err "Please check your $YELLOW\$CHARM_STORE$NORMAL variable value."