Xen 4.4 CentOS v2

Signed-off-by: David Scott <dave.scott@citrix.com>
Incorporate jonludlam's cleanups

Signed-off-by: David Scott <dave.scott@citrix.com>
Must not specify a fixed distribution
Merge pull request #522 from BobBall/jessie-fix

Must not specify a fixed distribution
Don't depend on ubuntu repo names in template
Merge pull request #523 from BobBall/jessie-fix

Don't depend on ubuntu repo names in template
Merge pull request #524 from djs55/centos-4.4

Xen 4.4 CentOS v2
Fix xenopsd-xenlight bugs

* Make dependency on xenopsd-xenlight conditional for xenserver-core
* When using xenopsd-xenlight we still need XCP_PATH set
Modprobe blktap/blkback as in xenopsd-xc