Change default value of "heartbeat_in_pthread" to False

As was reported in the related bug some time ago, setting that
option to True for nova-compute can break it as it's non-wsgi service.
We also noticed same problems with randomly stucked non-wsgi services
like e.g. neutron agents and probably the same issue can happen with
any other non-wsgi service.

To avoid that this patch changes default value of that config option
to be False.
Together with [1] it effectively reverts change done in [2] some time
ago.

[1] https://review.opendev.org/c/openstack/oslo.messaging/+/800621
[2] https://review.opendev.org/c/openstack/oslo.messaging/+/747395

Related-Bug: #1934937
Closes-Bug: #1961402

Change-Id: I85f5b9d1b5d15ad61a9fcd6e25925b7eeb8bf6e7