Test/API: use directories and files customization for supported images

Use directories and files customization in the compose request for image
types that support this customization (only ostree installer and raw
image do not support it).

Extend the instance verification to check for the custom directories and
files.

Extend the ostree commit verification to check for the custom
directories and files.

Signed-off-by: Tomáš Hozza <thozza@redhat.com>

test/cases/api.sh

@@ -330,6 +330,43 @@ EndOfMessage
 fi
 export SUBSCRIPTION_BLOCK
 
+# Define the customizations for the images here to not have to repeat them
+# in every image-type specific file.
+case "${IMAGE_TYPE}" in
+  # The Directories and Files customization is not supported for this image type.
+  "$IMAGE_TYPE_EDGE_INSTALLER")
+    DIR_FILES_CUSTOMIZATION_BLOCK=
+    ;;
+  *)
+    DIR_FILES_CUSTOMIZATION_BLOCK=$(cat <<EOF
+,
+    "directories": [
+      {
+        "path": "/etc/custom_dir/dir1",
+        "user": "root",
+        "group": "root",
+        "mode": "0775",
+        "ensure_parents": true
+      },
+      {
+        "path": "/etc/custom_dir2"
+      }
+    ],
+    "files": [
+      {
+        "path": "/etc/custom_dir/custom_file.txt",
+        "data": "image builder is the best\n"
+      },
+      {
+        "path": "/etc/custom_dir2/empty_file.txt"
+      }
+    ]
+EOF
+)
+    ;;
+esac
+export DIR_FILES_CUSTOMIZATION_BLOCK
+
 # generate a temp key for user tests
 ssh-keygen -t rsa-sha2-512 -f "${WORKDIR}/usertest" -C "usertest" -N ""