oeqa: Test failure/cleanup improvements
Currently, if qemu segfaults, the tests merrily continue trying to execute
which takes time for them to timeout and is a bit silly. Worse, no logs about
the segfault are shown to the user, its silent!
This patch tries to unravel the tangled web of issues and ensures that we:
* install a SIGCHLD handler which tells the user qemu exited
* check if qemu is running, if it isn't fail the test outright
* don't leave processes behind in sshcontrol which would hold
bitbake.lock and block shutdown
(From OE-Core rev:
77e9363feba53b72429154be5713c46b007ae0a4)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
