mgr/dashboard: fix for using '::' on hosts without ipv6

mgr/dashboard: fix for using '::' on hosts without ipv6

CherryPy throws an uncaught exception using '::' when the host does not
have an ipv6 loopback address. This is currently the case in kubernetes.
This patch disables the routine in cherrypy that performs the validation
that requested server ports are actually bound.

fixes: http://tracker.ceph.com/issues/38576

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
(cherry picked from commit 384d82a1bb1a3f0c2b1027968f03fe7834daad6a)

Conflicts:
	src/pybind/mgr/dashboard/module.py

Contextual conflict as >luminous had nearby SSL code that was never
backported.