Rename bin package into cmd

Most projects are migrating to entry_points now and the name of the
package is cmd. I renamed bin into cmd to keep consistency with other
projects.

Change-Id: Iab889123fb4836a42ed0ef52986ffa7648a140fa

setup.py

@@ -40,6 +40,6 @@ setuptools.setup(
     cmdclass=common_setup.get_cmdclass(),
     entry_points={
         'console_scripts':
-            ['marconi-server = marconi.bin.server:run']
+            ['marconi-server = marconi.cmd.server:run']
     }
 )