Explicitly marking google-cloud-core and google-api-core as "dev". (#4282)

This is to make it clear the code is between releases. Towards #4208.

See: https://snarky.ca/how-i-manage-package-version-numbers/

Author: dhermes

setup.py

@@ -65,7 +65,7 @@
 
 setup(
     name='google-api-core',
-    version='0.1.1',
+    version='0.1.2.dev1',
     description='Core Google API Client Library',
     long_description=README,
     namespace_packages=['google'],