Disable Ansible host key checking in BMRA container

This change avoids the need to copy SSH keys to the
provisioned hosts during BMRA provisioning by loading
the respective env variable inside the BMRA container.

Change-Id: I30cef25f65492da26435259b7f028f79c3b8cb01
Signed-off-by: Rihab Banday <rihab.banday@ericsson.com>
Reviewed-on: https://gerrit.opnfv.org/gerrit/c/kuberef/+/71081
Tested-by: jenkins-ci <jenkins-opnfv-ci@opnfv.org>
Reviewed-by: Michael Pedersen <michael.soelvkaer@gmail.com>
Reviewed-by: Georg Kunz <georg.kunz@est.tech>