qemuimage-testlib: Add extra debugging and sanity check

Check for a zero IP address since its clearly incorrect if that value
is found. Also add debugging for cases where we can't find the qemu
process. A process listing is handy to help understand what the problem
might be.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
runqemu: Improve error handling/exit codes

runqemu-internal is sourced so should be returning with an error code in
case of errors. runqemu needs to deal with this.

This patch fixes up the various error paths so we're consistent and get
a sane exit status for runqemu which helps a lot in its use in the qemu
runtime testing on the autobuilder.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>