Work around docker rate limit in CSITs

CSITs are failing regularly due to download rate limits that were
recently introduced on dockerhub.  Modified the yaml to download mariadb
from nexus3 instead of dockerhub.

Issue-ID: POLICY-2895
Change-Id: I554a230d11533245a4fe987a2ac809ffc69affc7
Signed-off-by: Jim Hahn <jrh3@att.com>
diff --git a/scripts/policy/docker-compose-all.yml b/scripts/policy/docker-compose-all.yml
index 55044c9..7b1f00a 100644
--- a/scripts/policy/docker-compose-all.yml
+++ b/scripts/policy/docker-compose-all.yml
@@ -18,7 +18,7 @@
 version: '2'
 services:
    mariadb:
-      image: mariadb:${POLICY_MARIADB_VER}
+      image: nexus3.onap.org:10001/mariadb:${POLICY_MARIADB_VER}
       container_name: mariadb
       hostname: mariadb
       command: ['--lower-case-table-names=1', '--wait_timeout=28800']