xenserver: Update interface-reconfigure and vif integration scripts.

xenserver: Update interface-reconfigure and vif integration scripts.

This patch updates the versions of the host integration scripts to
what is present in the recent XCP update and the next release of
XenServer (5.6). I think it probably works on 5.5 as well but I
haven't verified that.

These new versions support runtime selection of the Linux bridging vs
vswitch through the toolstack. The patch includes the necessary
reconfiguration (rewriting /etc/xensource/network.conf) to enable
vswitch in the RPM %post stage.

The RPM spec file integration is only lightly tested, seems to work
for me.

This commit is as provided by Ian Campbell, with a few minor tweaks:

    - Updated xenserver/automake.mk to distribute the added files.

    - Updated RPM spec file not to complain if the added files do
      not already exist (since they do not exist on XenServer 5.5.0).

    - Change location of dbcache back to /var/lib/openvswitch/dbcache
      so that this can coexist with our other internal builds.
      (Undoubtedly we will have to adopt the new location chosen by Ian
      eventually, however.)