Bug 1381770 - Enable multiple download retries in tooltool-download.sh. r=mshal

The scripts that use tooltool-download.sh don't run regularly, but when
they do, they might hit some download problems (the relengapi proxy
tends to be rather unreliable for some reason), and in that case, it
would be better to retry a few times, like other job types, rather than
fail directly.

--HG--
extra : rebase_source : d85797f8eebff9be5b8bfc45fc14dfaf8d5a59f3

taskcluster/scripts/misc/tooltool-download.sh

@@ -5,6 +5,6 @@ cd $WORKSPACE/build/src
 : TOOLTOOL_CACHE                ${TOOLTOOL_CACHE:=/home/worker/tooltool-cache}
 export TOOLTOOL_CACHE
 
-./mach artifact toolchain -v --tooltool-url=http://relengapi/tooltool/ --tooltool-manifest "${TOOLTOOL_MANIFEST}"${TOOLTOOL_CACHE:+ --cache-dir ${TOOLTOOL_CACHE}}
+./mach artifact toolchain -v --tooltool-url=http://relengapi/tooltool/ --tooltool-manifest "${TOOLTOOL_MANIFEST}"${TOOLTOOL_CACHE:+ --cache-dir ${TOOLTOOL_CACHE}} --retry 5
 
 cd $OLDPWD