Adjust how packer validate is called

Break out the `packer validate` call so we can:
- Disable errexit for _just_ the `packer validate` call so every path
  has an attempt at validation.
- Get the output of the `packer validate` call so that if there is a
  non-zero exit code we can output that along with the path being
  validated.

hooks/packer_validate.sh

@@ -4,6 +4,25 @@ set -o nounset
 set -o errexit
 set -o pipefail
 
+function packer_validate() {
+  local exit_code=0
+
+  packer init . > /dev/null
+
+  # Allow us to get output if the validation fails
+  set +o errexit
+  validate_output=$(packer validate "${ARGS[@]}" . 2>&1)
+  exit_code=$?
+  set -o errexit
+
+  if [[ $exit_code -ne 0 ]]; then
+    echo "Validation failed in $path"
+    echo -e "$validate_output"
+  fi
+
+  return $exit_code
+}
+
 if [ -z "$(command -v packer)" ]; then
   echo "packer is required"
   exit 1
@@ -24,8 +43,7 @@ for path in "${UNIQUE_PATHS[@]}"; do
   # Check each path in parallel
   {
     pushd "$path" > /dev/null
-    packer init . > /dev/null
-    packer validate "${ARGS[@]}" .
+    packer_validate
   } &
   pids+=("$!")
 done