Avoid need for GREP variable by avoiding GNUisms. The

Avoid need for GREP variable by avoiding GNUisms. The
only one we appear to have is use of '-q'. Replace it
with redirection to /dev/null.

Also avoid use of 'tail' by replacing with 'head' or
'grep' as appropriate.

Signed-off-by: Keir Fraser <keir@xensource.com>