Dbusers improvements

[jordic]

• Fixes bug https://github.com/plone/guillotina/issues/1069
• Be able to change a user password by patching it.

[codecov-io]

Codecov Report

Merging #1093 (0f7ec10) into master (3577d2c) will decrease coverage by 0.1%. The diff coverage is 88.9%.

@@           Coverage Diff            @@
##           master   #1093     +/-   ##
========================================
- Coverage    94.5%   94.5%   -0.0%     
========================================
  Files         341     342      +1     
  Lines       29273   29362     +89     
========================================
+ Hits        27658   27737     +79     
- Misses       1615    1625     +10     

Impacted Files	Coverage Δ
guillotina/contrib/dbusers/users.py	73.4% <70.6%> (-3.5%)	:arrow_down:
guillotina/contrib/dbusers/__init__.py	100.0% <100.0%> (ø)
guillotina/contrib/dbusers/adapters.py	100.0% <100.0%> (ø)
guillotina/contrib/dbusers/content/users.py	96.2% <100.0%> (+0.1%)	:arrow_up:
guillotina/contrib/dbusers/serializers.py	93.3% <100.0%> (+0.2%)	:arrow_up:
guillotina/contrib/dbusers/subscribers.py	93.6% <100.0%> (+0.3%)	:arrow_up:
guillotina/tests/dbusers/test_manage_groups.py	100.0% <100.0%> (ø)
guillotina/tests/dbusers/test_manage_users.py	100.0% <100.0%> (ø)