Implement access token to ease credential downloading.

Allow to query the web site without copy/pasting the user SSL certificates.
The query should be like:
curl -X POST -H "X-Access-Token: ACCESSTOKENVALUE" "https://slaposmaster.example.org/myspace/my_account/request-a-certificate/WebSection_requestNewCertificate"

Access token is destroyed after usage.
The token validity is one day.
Don't print partition informations if skipping processing this partition.
slapgrid: exception handling cleanup
slapgrid: grammar nazi, added comment
improved comment
SlapObject: extracted method _set_ownership
SlapObject: extracted method _additional_buildout_parameters
grid: removed no-op except..raise
removed unused exception object
tests: do not rotate supervisor logs when testing
fixed timing-sensitive tests
Removing check_periodicity behavior that might introduce weird use
cases (at least in this implementation). We might want to add a feature
request to get that behavior back, but in a more predictable way.
finished working on periodicity 'always force/always skip'
Do not encode None value.
slightly clearer function names
new command: "slapos configure client"
Merge branch 'cliff'

Conflicts:
	slapos/grid/SlapObject.py
updated CHANGES.txt
adding mock as a test dependency
changing 2 tests, making assertion on method call and not on side effects