XAPI-261/CA-96936: Make himn_only more general

To also manage the case of a localhost server.

Signed-off-by: Jerome Maloberti <jerome.maloberti@citrix.com>

Conflicts:
	ocaml/xapi/xapi_mgmt_iface.ml

Signed-off-by: Jerome Maloberti <jerome.maloberti@citrix.com>
XOP-261/CA-96936: Prevent multiple starts of localhost server

Signed-off-by: Jerome Maloberti <jerome.maloberti@citrix.com>
XOP-261/CA-96936: Issue a warning in case of multiple starts of HIMN server

Signed-off-by: Jerome Maloberti <jerome.maloberti@citrix.com>
CA-96936/XOP-261: himn interface should not be started if the host is
already listening on ANY.

Signed-off-by: Jerome Maloberti <jerome.maloberti@citrix.com>
Merge pull request #1032 from jeromemaloberti/XOP-261-master

CA-96936/XOP-261: Reinstate the server on 127.0.0.1 when no management interface is defined