Stop accessing unbound variables

The kayobe-env script would try accessing $1 which is an unbound
variable if no argument is passed. This fails when `set -u` is set.

Also refactor usage output into a function. As a side effect, a missing
argument to --environment now causes the script to properly exit with an
error.

Change-Id: I9a44578196086ec24de80b992fed385826778feb

kayobe-env

@@ -33,15 +33,17 @@ base_path=$(realpath $KAYOBE_CONFIG_ROOT/../../)
 export KOLLA_SOURCE_PATH=${KOLLA_SOURCE_PATH:-${base_path}/src/kolla-ansible}
 export KOLLA_VENV_PATH=${KOLLA_VENV_PATH:-${base_path}/venvs/kolla-ansible}
 
-if [ "$1" = "--environment" ]; then
-  if [ "$#" -ne 2 ]; then
-    echo "usage: ${BASH_SOURCE[0]:-${(%):-%x}} [--environment <env-name>]"
-  else
-    kayobe_env="$2"
+function usage {
+  echo "usage: ${BASH_SOURCE[0]:-${(%):-%x}} [--environment <env-name>]"
+  return 1
+}
 
+if [[ "$#" -ge 1 ]]; then
+  if [[ "$1" = "--environment" && "$#" -eq 2 ]]; then
+    kayobe_env="$2"
     # Look for existing Kayobe environments
-    if [ -d "${KAYOBE_CONFIG_PATH}/environments" ]; then
-      if [ -d "${KAYOBE_CONFIG_PATH}/environments/${kayobe_env}" ]; then
+    if [[ -d "${KAYOBE_CONFIG_PATH}/environments" ]]; then
+      if [[ -d "${KAYOBE_CONFIG_PATH}/environments/${kayobe_env}" ]]; then
         export KAYOBE_ENVIRONMENT="${kayobe_env}"
         echo "Using Kayobe environment ${KAYOBE_ENVIRONMENT}"
       else
@@ -52,8 +54,7 @@ if [ "$1" = "--environment" ]; then
       echo "Cannot find environments folder in ${KAYOBE_CONFIG_PATH}"
       return 1
     fi
+  else
+    usage
   fi
-elif [ "$#" -ne 0 ]; then
-  echo "usage: ${BASH_SOURCE[0]:-${(%):-%x}} [--environment <env-name>]"
-  return 1
 fi