Add support for classmethod console scripts

 * Previously console_scripts could only reference functions:

     script_name = package.name:function_name

   This change adds support for classmethods:

     script_name = package.name:ClassName.classmethod_name

   This change is necessary to support a Neutron use-case.

 * Fixes bug 1206734

Change-Id: I9509d3f2cea29fee5696936dbbb1d507764f1e81
Merge "Add support for classmethod console scripts"