xenserver: Crossport "master" interface-reconfigure to "citrix".
This commit copies the interface-reconfigure script from "master" into
"citrix" and fixes up a few incompatibilities: the location of ovs-cfg-mod,
which in master is in /usr/bin and in citrix is in /root/vswitch/bin, and
the RPM spec file fragments needed to initialize the database cache.
The purpose of this commit is to obtain the bug fixes that have been
applied (mainly by Ian Campbell) to "master" but which are not in "citrix".
It's difficult to understand the changes from this commit alone. It is
more meaningful to compare the resulting files against those currently
on the master branch.