change to environment.rst heat doc
change to environment.rst heat doc

corrected typo for signalling (signaling)
changed to behavior for consistency
fixed capitalization to comply with doc conventions
https://wiki.openstack.org/wiki/Documentation/Conventions

Change-Id: I21788bb16877d5034e2e2c5e6905229f43342efb

gonzolino/heat,openstack/heat,miguelgrinberg/heat,pratikmallya/heat,pratikmallya/heat,dragorosson/heat,steveb/heat,takeshineshiro/heat,gonzolino/heat,dims/heat,rh-s/heat,pshchelo/heat,cryptickp/heat,openstack/heat,srznew/heat,cryptickp/heat,jasondunsmore/heat,maestro-hybrid-cloud/heat,maestro-hybrid-cloud/heat,takeshineshiro/heat,rdo-management/heat,pshchelo/heat,srznew/heat,dims/heat,jasondunsmore/heat,steveb/heat,cwolferh/heat-scratch,miguelgrinberg/heat,dragorosson/heat,rh-s/heat,noironetworks/heat,rdo-management/heat,noironetworks/heat,cwolferh/heat-scratch