Add code tag for from_task_with_args() docstring
Add code tag for from_task_with_args() docstring

Simply adding an extra colon in the from_task_with_args docstring to
make the examples show up as code in the rendered documentation.

Co-Author: Qiming Teng
Change-Id: Ia1704a2f2517e2de2fb4f300979f63fbec0e9f7a

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