stubdom: Fix stubdom-dm using "grep" improperly

stubdom: Fix stubdom-dm using "grep" improperly

stubdom-dm uses "grep" on "xm list" output to determine whether it is
already running. The existing behavior is to use "grep $domname-dm" but
this will result in a false-positive in the case of another domU running
whose name ends with the full new name; for instance, if "abctest-dm" is
running, a new "test-dm" will spin forever, waiting for it the end.

Any easy fix is to have it use "grep -w" instead of "grep", searching
for the whole word only.

It also might be worth considering a switch to "xl list" from "xm list",
here and in other places.

Signed-off-by: John Weekes <lists.xen@nuclearfallout.net>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>