TT#121955 build: detect release_uuid empty value

> [info     ] request_started [django_structlog.middlewares.request] ip=192.168.208.21 request=POST /jenkinsbuildinfo/ request_id=e435d38f-f690-4ba6-8b58-01ef76d0d988 user_agent=python-requests/2.21.0 user_id=None
> {'request_id': 'e435d38f-f690-4ba6-8b58-01ef76d0d988', 'user_id': None, 'ip': '192.168.208.21', 'release_uuid': '$release_uuid', 'release': 'release-mr7.5-update', 'event': 'BuildRelease not found', 'logger': 'build.signals', 'level': 'error'}

Change-Id: I0aa2eb7690d52becbe4ae556e561f87017b50d16

build/signals.py

@@ -68,7 +68,7 @@ def jbi_manage(sender, **kwargs):
     if jbi.jobname in settings.BUILD_RELEASE_JOBS:
         if not release.startswith("release-"):
             release = "release-{}".format(jbi.param_release)
-    if jbi.param_release_uuid in [None, "none", ""]:
+    if jbi.param_release_uuid in [None, "none", "", "$release_uuid"]:
         log.debug("no ReleaseBuild link, skip")
         return
     try: