sss_obfuscate: do not fail if sssd.conf contains non-ascii characters
    
    If sssd.conf contains non-ascii characters (e.g. `# el selinux lo bloquea cuando
    está en enforcing`) then sss_obfuscate fails on python2, truncating the whole
    configuration file.
    
    ```
    Enter password:
    Re-enter password:
    Traceback (most recent call last):
      File "/sbin/sss_obfuscate", line 122, in <module>
        ret = main()
      File "/sbin/sss_obfuscate", line 112, in main
        sssdconfig.write()
      File "/usr/lib/python2.7/site-packages/SSSDConfig/__init__.py", line 1526, in write
        output = self.dump(self.opts).encode('utf-8')
    UnicodeDecodeError: 'ascii' codec can't decode byte 0xc5 in position 977: ordinal not in range(128)
    
    -rw-------. 1 root root 0 Oct 10 09:09 /etc/sssd/sssd.conf
    ```
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/4030
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>