qerror: add check-qerror.sh to verify alphabetical order

We're supposed to keep qerror definitions and table entries in
alphabetical order.  In practice this is not checked.

I haven't found a nice way to integrate this into the makefile yet but
we can at least have this script which verifies that qerrors are in
alphabetical order.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
