Daily Deja Dup failure with "Failed with an unknown error."

[Michal Pasniewski]

Daily backup fails with:
```
Traceback (innermost last):
  File "/usr/bin/duplicity", line 1555, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1541, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1393, in main
    do_backup(action)
  File "/usr/bin/duplicity", line 1511, in do_backup
    full_backup(col_stats)
  File "/usr/bin/duplicity", line 572, in full_backup
    globals.backend)
  File "/usr/bin/duplicity", line 454, in write_multivol
    (tdp, dest_filename, vol_num)))
  File "/usr/lib/python2.7/dist-packages/duplicity/asyncscheduler.py", line 146, in schedule_task
    return self.__run_synchronously(fn, params)
  File "/usr/lib/python2.7/dist-packages/duplicity/asyncscheduler.py", line 172, in __run_synchronously
    ret = fn(*params)
  File "/usr/bin/duplicity", line 453, in <lambda>
    vol_num: put(tdp, dest_filename, vol_num),
  File "/usr/bin/duplicity", line 342, in put
    backend.put(tdp, dest_filename)
  File "/usr/lib/python2.7/dist-packages/duplicity/backend.py", line 395, in inner_retry
    % (n, e.__class__.__name__, util.uexc(e)))
  File "/usr/lib/python2.7/dist-packages/duplicity/util.py", line 79, in uexc
    return ufn(unicode(e).encode('utf-8'))
 UnicodeDecodeError: 'ascii' codec can't decode byte 0xe2 in position 37: ordinal not in range(128)
```

Ubuntu 18.04.3 LTS
deja-dup 37.1-2fakesync1ubuntu0.1
duplicity 0.7.17-0ubuntu1.1

[Michael Terry (mterry)]

This is fixed in 19.10 by using the python3 version of duplicity.

You can get the fix on 18.04 by using the snap version of Deja Dup:
snap install deja-dup --classic