oeqa/qemurunner: Improve handling of run_serial for shutdown commands

When running a shutdown command, the serial port can close without the
command returning. This is seen as the socket being readable but having
no data. Change the way this case is handled in the code to avoid
tracebacks.

(From OE-Core rev: 396a3ba884820d040c91f7592daf20ac28c49b5d)

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

meta/lib/oeqa/utils/qemurunner.py

@@ -73,6 +73,8 @@ class QemuRunner:
         self.monitorpipe = None
 
         self.logger = logger
+        # Whether we're expecting an exit and should show related errors
+        self.canexit = False
 
         # Enable testing other OS's
         # Set commands for target communication, and default to Linux ALWAYS
@@ -543,6 +545,7 @@ class QemuRunner:
             self.thread.join()
 
     def allowexit(self):
+        self.canexit = True
         if self.thread:
             self.thread.allowexit()
 
@@ -604,7 +607,9 @@ class QemuRunner:
                     if re.search(self.boot_patterns['search_cmd_finished'], data):
                         break
                 else:
-                    raise Exception("No data on serial console socket")
+                    if self.canexit:
+                        return (1, "")
+                    raise Exception("No data on serial console socket, connection closed?")
 
         if data:
             if raw: