xenapi: Get rid of internal xapi interface

OpenStack VM had 4 interfaces, from which eth0 was not used at all. This
change removes the non-used interface, thus devstack is providing the
same architecture as described in the official documentation:

    http://goo.gl/dmrNF

Related to blueprint xenapi-devstack-cleanup

Change-Id: I73c9751ade6f4786b8b682a1994cb87f0a624379
Move network setup to one place

Change-Id: Id1056a3d632233231b0c0e36be2b7eb17d620169
Introduce variables for device numbers

Change-Id: I7f1de22ab5316fcc658106840606c28858d53224
Remove interfaces.in template

Change-Id: I610e59d90bda026460c1c6519f824708e24178cb
Renumbering networks

It seems, that if you attach devices 1, 2 and 3, they will appear as
eth0, eth1 and eth2 - they will be re - ordered by linux

Change-Id: I9b8665b94303b2406fc910fdb862f4f716909cf3
Add int br device nr

Change-Id: I7f7ee7022a58c47e0ec74ad3be614fcaa0de55d2
Swap interfaces - so it aligns with the official docs

Change-Id: Id5e6ca3a2c1c74047bb1d3859f4a6fa518f1d49e