scripts/runqemu: provide better error message on runqemu ifup fail
If runqemu-ifup fails hen running testimage, a rather cryptic error
regarding "no tty present" is displayed. If this step fails, we
should at least point the user at runqemu-gen-tapdevs. A quick search
of this term in the manual will lead them to "Enabling Runtime Tests
on QEMU" which should give them all the info they need.
Signed-off-by: Stephano Cetola <stephano.cetola@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
