[PR #3531/d1f820ed backport][stable-1] Fix shellcheck error (#3532)

* Fix shellcheck error. (#3531)

(cherry picked from commit d1f820ed06)

* Vendored ipaddress is still present in stable-1 branch, so use that one.

Co-authored-by: Felix Fontein <felix@fontein.de>

tests/utils/shippable/shippable.sh

@@ -50,7 +50,7 @@ function retry
         echo "@* -> ${result}"
     done
     echo "Command '@*' failed 3 times!"
-    exit -1
+    exit 255
 }
 
 command -v pip