libxl: revert 326a7b74

libxl: revert 326a7b74

When running libxl from a driver domain there's no xenstore pid file
(because xenstore is not running on the driver domain). Also, at that
point in libxl initialization there's no way to know wether libxl is
running on a domain different than Dom0, so just revert the change in
order to allow libxl to work on driver domains.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>