Update Xen RA to use xl instead of the deprecated xm

First commit replaces the use of the xm command line tool with xl.

For more details, see:

- http://wiki.xen.org/wiki/XL#Upgrading_from_xend
- http://wiki.xen.org/wiki/MigrationGuideToXen4.1

Also comes with a second commit which cleans up trailing whitespace in the RA.