Pin os_heat role to the version with working policy

Pin os_heat role to the version with working policy

Upstream change modifying policy.json results in failures with
several heat test case failures with functest healthcheck.

https://review.openstack.org/#/c/526306/

Using the policy.json from the earlier commit seems to solve
the failures which is this

https://git.openstack.org/cgit/openstack/openstack-ansible-os_heat/commit/?id=0b3eb9348d55d6b1cf077a2c45b297f9a1be730d

Change-Id: Iaac0911e73743d1b628cc8d4abe460a0a2a66a84
Signed-off-by: Fatih Degirmenci <fdegir@gmail.com>