Bug 1593891 - Allow running periodic-updates that do not trigger a bu…

…ild. r=sfraser

When these land for Thunderbird, I set the keyword to prevent a build manually.
periodic_file_updates.sh supports that with "-d", but the runme.sh wrapper
does not have a mechanism to set it.
This patch follows the environment variable precedent used for the other
script parameters.

Differential Revision: https://phabricator.services.mozilla.com/D52024

taskcluster/docker/periodic-updates/README.md

@@ -20,6 +20,9 @@ Likewise for `DO_HPKP` and the HPKP checks, and `DO_BLOCKLIST` and the
 blocklist checks. Environment variables are used rather than command line
 arguments to make constructing taskcluster tasks easier.
 
+To prevent a full build when landing with Phabricator, set the `DONTBUILD`
+environment variable.
+
 ==Background==
 
 These scripts have been moved from

taskcluster/docker/periodic-updates/runme.sh

@@ -47,6 +47,11 @@ then
   PARAMS="${PARAMS} --suffix-list"
 fi
 
+if [ -n "${DONTBUILD}" ]
+then
+  PARAMS="${PARAMS} -d"
+fi
+
 
 export ARTIFACTS_DIR="/home/worker/artifacts"
 mkdir -p "$ARTIFACTS_DIR"