Disable doc building

Building docs involves importing 'heat.doc.resources' (from
doc/source/conf.py) which leads to the following:

>>> __import__('heat.doc.resources', None, None, ['setup'])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "heat/doc/resources.py", line 17, in <module>
    from heat.engine import resources
  File "heat/engine/resources/__init__.py", line 15, in <module>
    from heat.openstack.common import log as logging
  File "heat/openstack/common/log.py", line 41, in <module>
    from oslo.config import cfg
ImportError: No module named config

This starts to explode the build-requires; at least
 - python-oslo-config
 - python-netaddr
 - python-paste
 - python-paste-deploy
 - python-iso8601
 - python-lxml
 - python-webob
 - keystoneclient.contrib.ec2

are required (I stopped adding things there)

Take the easy route, and skip doc generation

Conflicts:
	openstack-heat.spec