Raise ansible forks for CI test config

As we raised the flavor from small to standard, raise the ansible
forks from default 5 to 20 to speed up deployment.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

tests/ansible.cfg

 [ssh_connection]
 pipelining=True
 [defaults]
+forks = 20
 host_key_checking=False
 gathering = smart
 fact_caching = jsonfile