Add xapi toolstack and a set of dependent libraries and services

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
xapi-tapctl: fix the uninstall target

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Update xapi to 1.9.55, with a (hopefully fixed) configure script

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Update xapi to 1.9.56

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #2700 from djs55/add-xapi

Add xapi toolstack and a set of dependent libraries and services