Return the OS version information from the device.

def get_os_version(self, version_text):
        """Return the OS version information from the device."""
        os_version = None
        if version_text is None:
            return os_version
        match = re.search(self.version_re, version_text, re.MULTILINE)
        if match:
            os_version = match.group(1)

        return os_version