Fixes solum_api Listening on 127.0.0.1

The default kolla-ansible deployment of solum_api do not provide a value for 'host' variable in
[api] section of the solum.conf
This causes the solum_api service to fallback to default host 127.0.0.1, making haproxy unable to
provide services.

This fix adds value for 'host' variable, so the solum_api service able to listen on provided ip,
making it available to services like haproxy accessing the service remotely

Closes-Bug: 1909986
Change-Id: I38a4ecab071306143952c8036830318c476797f2