tf-a-daily: Run tests using low LAVA priority

As this is background daily job, on average, there's low expectation of
its result to arrive at a particular time every day. So, make test jobs
submitted by it to have low priority, to not complete e.g. with test
jobs for Gerrit patches, results of which developers eagerly await.

Implements https://linaro.atlassian.net/browse/TFC-370

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I7d8d83da3f0fe3b794a2d8901b52d482e2a5df6a
diff --git a/tf-a-daily.yaml b/tf-a-daily.yaml
index 7827fbd..4f1d48b 100644
--- a/tf-a-daily.yaml
+++ b/tf-a-daily.yaml
@@ -34,6 +34,9 @@
             name: CI_REFSPEC
             default: '+refs/heads/master:refs/remotes/origin/master'
         - string:
+            name: LAVA_PRIORITY
+            default: 'low'
+        - string:
             name: SHARE_FOLDER
             default: '/srv/shared/${JOB_NAME}/${BUILD_NUMBER}'
             description: 'Folder containing shared repositories for downstream pipeline jobs'