Add missing lines for fixing Singularity volumes.

These should have been included in #4180.

lib/galaxy/tools/deps/containers.py

@@ -536,7 +536,8 @@ def prop(name, default):
             raise Exception("Cannot containerize command [%s] without defined working directory." % working_directory)
 
         volumes_raw = self._expand_volume_str(self.destination_info.get("singularity_volumes", "$defaults"))
-        volumes = docker_util.DockerVolume.volumes_from_str(volumes_raw)
+        preprocessed_volumes_str = preprocess_volumes(volumes_raw, self.container_type)
+        volumes = docker_util.DockerVolume.volumes_from_str(preprocessed_volumes_str)
 
         singularity_target_kwds = dict(
             singularity_cmd=prop("cmd", singularity_util.DEFAULT_SINGULARITY_COMMAND),