hwid: Moves exported interfaces into `hwid_utils` module.

This CL moves exported interfaces and constants from
`cros.factory.hwid.v3.common` to `cros.factory.hwid.v3.hwid_utils`.

The module `cros.factory.hwid.v3.common` should contain only HWID
framework internal used classes, and all the exported interfaces should
be located in `cros.factory.hwid.v3.hwid_utils`.

TEST=make test
BUG=chromium:797645

Change-Id: I4ff8376aa4f6b079431d8d173f847e22fffe085e
Reviewed-on: https://chromium-review.googlesource.com/844296
Commit-Ready: Yong Hong <yhong@google.com>
Tested-by: Yong Hong <yhong@google.com>
Reviewed-by: Yong Hong <yhong@google.com>
diff --git a/py/tools/regcode.py b/py/tools/regcode.py
index c25632b..7066e05 100755
--- a/py/tools/regcode.py
+++ b/py/tools/regcode.py
@@ -16,7 +16,7 @@
 
 import factory_common  # pylint: disable=W0611
 from cros.factory.device import device_utils
-from cros.factory.hwid.v3 import common as hwid_common
+from cros.factory.hwid.v3 import hwid_utils
 from cros.factory.proto import reg_code_pb2
 from cros.factory.test.rules import registration_codes
 from cros.factory.test.rules.registration_codes import RegistrationCode
@@ -104,7 +104,7 @@
     if sys_utils.InChroot():
       options.project = BuildBoard().short_name
     else:
-      options.project = hwid_common.ProbeProject()
+      options.project = hwid_utils.ProbeProject()
   logging.info('Device name: %s', options.project)
 
   rw_vpd = None