tf-static-checks: include REPO_UNDER_TEST choice parameter

Currently the tf-static-checks job can only (static)check the core project
trusted-firmare-a, but job must be to check at least the tf-a-tests
repository. This commit enables a new choice parameter, REPO_UNDER_TEST,
defaulting to trusted-firmware-a but including the tf-a-tests
repository in the choice list.

Enabling another choice project, implies repository cloning and
including gerrit related parameters, TFTF_GERRIT_*, so this changes
are part of the commit.

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: I468124a07542f72e2c8a16191b4ee701f8d98827
diff --git a/tf-static-checks/postbuild.groovy b/tf-static-checks/postbuild.groovy
index d88c9a1..7cdaa88 100644
--- a/tf-static-checks/postbuild.groovy
+++ b/tf-static-checks/postbuild.groovy
@@ -19,7 +19,8 @@
   return url
 }
 
-def artifact = "trusted-firmware-a/static-checks.log"
+def repo_under_test = manager.build.buildVariables.get('REPO_UNDER_TEST')
+def artifact = "${repo_under_test}/static-checks.log"
 def jobUrl = manager.hudson.getRootUrl() + "${manager.build.url}artifact/${artifact}"
 def url = new URL(jobUrl)
 def realUrl = findRealUrl(url)