scritps/runqemu: Ensure we only have two serial ports

I have a theory that some of the console boot issues we're seeing are due to
starting images with three serial ports yet only starting gettys on two of them.

This means that occasionally, depending on the port numbering we may not get
a login prompt on the console we expect it on.

To fix this, change the runqemu code so that if serial ports are passed in on
the commandline (as is the case in automated testing), we don't add any other
GUI serial consoles.

We do need to make sure we do have at least two serial ports since we don't want
getty timeout warnings.

(From OE-Core rev: 44e1279970d306b0da4fcc11f9e780915f481819)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 1b0348535dce3b776efbcf26406b94730a51eb85)
Signed-off-by: Ming Liu <liu.ming50@gmail.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

scripts/runqemu

@@ -1408,6 +1408,19 @@ to your build configuration.
             for entry in self.get('SERIAL_CONSOLES').split(' '):
                 self.kernel_cmdline_script += ' console=%s' %entry.split(';')[1]
 
+        # We always wants ttyS0 and ttyS1 in qemu machines (see SERIAL_CONSOLES).
+        # If no serial or serialtcp options were specified, only ttyS0 is created
+        # and sysvinit shows an error trying to enable ttyS1:
+        #     INIT: Id "S1" respawning too fast: disabled for 5 minutes
+        serial_num = len(re.findall("-serial", self.qemu_opt))
+
+        # Assume if the user passed serial options, they know what they want
+        # and pad to two devices
+        if serial_num == 1:
+            self.qemu_opt += " -serial null"
+        elif serial_num >= 2:
+            return
+
         if self.serialstdio == True or self.nographic == True:
             self.qemu_opt += " -serial mon:stdio"
         else:
@@ -1419,10 +1432,6 @@ to your build configuration.
 
                 self.qemu_opt += " %s" % self.get("QB_SERIAL_OPT")
 
-        # We always wants ttyS0 and ttyS1 in qemu machines (see SERIAL_CONSOLES).
-        # If no serial or serialtcp options were specified, only ttyS0 is created
-        # and sysvinit shows an error trying to enable ttyS1:
-        #     INIT: Id "S1" respawning too fast: disabled for 5 minutes
         serial_num = len(re.findall("-serial", self.qemu_opt))
         if serial_num < 2:
             self.qemu_opt += " -serial null"