Move volume parsing to config.types module

This removes the last of the old service.ConfigError

Signed-off-by: Daniel Nephin <dnephin@docker.com>

tests/acceptance/cli_test.py

@@ -37,7 +37,7 @@ def start_process(base_dir, options):
 def wait_on_process(proc, returncode=0):
     stdout, stderr = proc.communicate()
     if proc.returncode != returncode:
-        print(stderr)
+        print(stderr.decode('utf-8'))
         assert proc.returncode == returncode
     return ProcessResult(stdout.decode('utf-8'), stderr.decode('utf-8'))