runqemu: keep generating tap devices

in case there is no tap device the script tries to
generate a new one.
The new device is then unguarded for a moment, so
the newly generated device could be acquired
by a different instance or user, before it is locked to
the instance with acquire_taplock.
To fix that keep generating new tap devices in case
the lock can't be acquired up to 5 times.
If no tap device can be locked it fails in the existing
error handling

(From OE-Core rev: 23876576d054ebbab9b02c0012782aa56feda123)

Signed-off-by: Konrad Weihmann <kweihmann@outlook.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/runqemu

@@ -1195,6 +1195,7 @@ to your build configuration.
             uid = os.getuid()
             logger.info("Setting up tap interface under sudo")
             cmd = ('sudo', self.qemuifup, str(gid))
+            for _ in range(5):
                 try:
                     tap = subprocess.check_output(cmd).decode('utf-8').strip()
                 except subprocess.CalledProcessError as e:
@@ -1202,9 +1203,12 @@ to your build configuration.
                     sys.exit(1)
                 lockfile = os.path.join(lockdir, tap)
                 self.taplock = lockfile + '.lock'
-            self.acquire_taplock()
+                if self.acquire_taplock():
                     self.cleantap = True
                     logger.debug('Created tap: %s' % tap)
+                    break
+                else:
+                    tap = None
 
         if not tap:
             logger.error("Failed to setup tap device. Run runqemu-gen-tapdevs to manually create.")