This commit handles deployment of TLS certificates on control nodes for
use by HAProxy, when kolla_enable_tls_external is True and a new
variable, kolla_tls_cert, is populated with the contents of the
certificate file.
Story: 2001680
Task: 6786
Change-Id: I78df9e2d7acb96a4358ba3819a2dfc65e8c261d5