Fix heat service availability config option name

heat service config option name registered in
Tempest's service_available group is 'heat_plugin' which
is not consistent with all other service_available config
option.

This config option is used by other tempest plugin to test the heat.
One good example is congress-tempest-plugin which has heat tests[1]
and those test are being skipped based on this config option.

But setting of this config option in congress devstack plugin
is done based on service name (heat not heat_plugin)[2]. and same name
is used on devstack side also[3].

We had same issue on aodh side also which is being fixed in
- https://review.openstack.org/#/c/536741/

This patch fixes this issue in heat-tempest-plugin also by
renaming the config option to 'heat' and keep the old name support also
with deprecation warning.
Related-Bug: #1743688

[1] http://git.openstack.org/cgit/openstack/congress-tempest-plugin/tree/congress_tempest_plugin/tests/scenario/congress_datasources/test_heat.py#n32
[2] https://github.com/openstack/congress/blob/df0f555f3166344b726fbfd2356e3a7d897cf228/devstack/plugin.sh#L87
[3] https://github.com/openstack-dev/devstack/blob/0c6208c6a07b0616b5982b6e9e7c8216397d49e3/lib/tempest#L550

Change-Id: Ibe080d08a854db1a3e7246ef60a3a14efdc2f40f
1 file changed