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: 5c04b1ca1e989f569d5755a646734d01a0c56cae)

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

meta/lib/oeqa/utils/sshcontrol.py

@@ -42,7 +42,7 @@ class SSHProcess(object):
             with open(self.logfile, "a") as f:
                f.write("%s" % msg)
 
-    def run(self, command, timeout=None, logfile=None):
+    def _run(self, command, timeout=None, logfile=None):
         self.logfile = logfile
         self.starttime = time.time()
         output = ''
@@ -79,8 +79,18 @@ class SSHProcess(object):
 
         self.status = self.process.wait()
         self.output = output.rstrip()
-        return (self.status, self.output)
 
+    def run(self, command, timeout=None, logfile=None):
+        try:
+            self._run(command, timeout, logfile)
+        except:
+            # Need to guard against a SystemExit or other exception occuring whilst running
+            # and ensure we don't leave a process behind.
+            if self.process.poll() is None:
+                self.process.kill()
+                self.status = self.process.wait()
+            raise
+        return (self.status, self.output)
 
 class SSHControl(object):
     def __init__(self, ip, logfile=None, timeout=300, user='root', port=None):