pwclient: fix handling of UTF-8 char in submitter name

pwclient: fix handling of UTF-8 char in submitter name

This patch fixes following bug in 'list':

---8<---
# pwclient list -p uboot -w andreas.devel | grep New
Traceback (most recent call last):
  File "/Users/andreas/bin/pwclient", line 463, in <module>
    main()
  File "/Users/andreas/bin/pwclient", line 411, in main
    action_list(rpc, filt, submitter_str, delegate_str)
  File "/Users/andreas/bin/pwclient", line 182, in action_list
    (person['name'], person['email'])
UnicodeEncodeError: 'ascii' codec can't encode character u'\xdf' in
position 32: ordinal not in range(128)
--->8---

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>