pick gerrit choosing-strategy as scm checkout strategy

Currently, Open CI checkouts a branch, either integration or master,
instead of user's MR refspec (GERRIT_REFSPEC), effectively not
testing users patches. This change indicates the scm plugin to use
gerrit as choosing strategy, which indicates the way it checkouts,
taking into consideration user's patch.

Also, a minor patch does a fix on the tf-a-tests repo, pointing to
review.trustedfirmware.org instead of git.trustedfirmware.org, the
former is the right repository to checkout gerrit refspecs.

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: Iacf880f13fa76db473ef49c6de772404933a7406
diff --git a/tf-static-checks.yaml b/tf-static-checks.yaml
index 2f01de7..81ab262 100644
--- a/tf-static-checks.yaml
+++ b/tf-static-checks.yaml
@@ -21,6 +21,7 @@
             branches:
                 - ${TF_GERRIT_BRANCH}
             basedir: trusted-firmware-a
+            choosing-strategy: gerrit
             skip-tag: true
             shallow-clone: false
             wipe-workspace: false
@@ -34,6 +35,7 @@
             branches:
                 - ${TFTF_GERRIT_BRANCH}
             basedir: tf-a-tests
+            choosing-strategy: gerrit
             skip-tag: true
             shallow-clone: false
             wipe-workspace: false