test: switch to the "nobody" user so file read/only vs read/write checks work
test: switch to the "nobody" user so file read/only vs read/write checks work

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

djs55/ocaml-vhd,xapi-project/ocaml-vhd