xenserver: modify module spec file

xenserver: modify module spec file

Based on feedback from Citrix about building for multiple kernels,
the spec file has been modified to take three arguments on the
command line: kernel_name, kernel_version and kernel_flavor.

The kernel_flavor is either xen or kdump. The kernel_name is the
Name value embedded in the kernel rpm and the kernel_version
is Version-Release values embedded in the kernel rpm. The
xen_version is calculated.

The INSTALL document has been updated to reflect these changes.

Signed-off-by: Sajjad Lateef <slateef@nicira.com>
(cherry picked from commit b11e4aa7e92854612a4d139b8a620d036a5d41a2)