exporter: check ser2net version in exporter

The following ser2net versions return nonzero even on a successful use
of the -v flag to get the version:

v4.4.0
v4.5.0
v4.5.1
v4.6.0
v4.6.1

This was fixed in v4.6.2, which was only recently released. Modify
_start() so that it uses subprocess.run() to capture stdout and the
returncode, then check against the version and effectively ignore the
return value if there's a match. If the ser2net version is one of the
unaffected ones (e.g. v4.6.2) and still returns nonzero, then raise an
ExporterError.

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>

Author: threexc

labgrid/remote/exporter.py

@@ -225,8 +225,17 @@ def _start(self, start_params):
         self.port = get_free_port()
 
         # Ser2net has switched to using YAML format at version 4.0.0.
-        _, _, version = str(subprocess.check_output([self.ser2net_bin,'-v'])).split(' ')
+        result = subprocess.run([self.ser2net_bin,'-v'], capture_output=True, text=True)
+        _, _, version = str(result.stdout).split(' ')
         major_version = version.split('.')[0]
+
+        # There is a bug in ser2net between 4.4.0 and 4.6.1 where it
+        # returns 1 on a successful call to 'ser2net -v'. We don't want
+        # a failure because of this, so raise an error only if ser2net
+        # is not one of those versions.
+        if version.strip() not in ["4.4.0", "4.5.0", "4.5.1", "4.6.0", "4.6.1"] and result.returncode == 1:
+            raise ExporterError(f"ser2net {version} returned a nonzero code during version check.")
+
         if int(major_version) >= 4:
             cmd = [
                 self.ser2net_bin,