Add the xapi statistics gathering daemon

Signed-off-by: David Scott <dave.scott@citrix.com>
xapi-rrdd depends on oclock

Signed-off-by: David Scott <dave.scott@citrix.com>
Update to xapi-rrdd.0.9.8

Signed-off-by: David Scott <dave.scott@citrix.com>
Merge pull request #2839 from djs55/xapi-rrdd

Add the xapi statistics gathering daemon