Metal3: Align mariadb image repo definition for proj var and remove extra space

Change-Id: I794cfcbd5b6a88fcf3036f141640e6bf991808eb
diff --git a/jjb/metal3/projects.yml b/jjb/metal3/projects.yml
index 869e60d..bf391ff 100644
--- a/jjb/metal3/projects.yml
+++ b/jjb/metal3/projects.yml
@@ -76,7 +76,7 @@
           repo: ironic-image
       - ironic_ipa_downloader:
           repo: ironic-ipa-downloader
-      -  mariadb-image:
+      - mariadb_image:
           repo: mariadb-image
     image_os:
       - ubuntu