tests: fix spurious test failure

Failure introduced in commit 3a092f38.

* tests/xml2sexprdata/xml2sexpr-boot-grub.sexpr: Fix typo.

tests/xml2sexprdata/xml2sexpr-boot-grub.sexpr

-(vm (name 'pvtest')(memory 420)(maxmem 420)(vcpus 2)(uuid '596a5d21-71f4-8fb2-e068-e2386a5c413e')(on_poweroff 'destroy')(on_reboot 'destroy')(on_crash 'destroy')(image (linux (kernel '/usr/lib/xen/boot/pv-grub-x86_64.gz')(args (hd0,0)/grub/menu.lst)))(device (vbd (dev 'xvda')(uname 'phy:/dev/MainVG/GuestLV')(mode 'w'))))
\ No newline at end of file
+(vm (name 'pvtest')(memory 420)(maxmem 420)(vcpus 2)(uuid '596a5d21-71f4-8fb2-e068-e2386a5c413e')(on_poweroff 'destroy')(on_reboot 'destroy')(on_crash 'destroy')(image (linux (kernel '/usr/lib/xen/boot/pv-grub-x86_64.gz')(args '(hd0,0)/grub/menu.lst')))(device (vbd (dev 'xvda')(uname 'phy:/dev/MainVG/GuestLV')(mode 'w'))))
\ No newline at end of file