Create system tests for collect anonymous usage statistics feature

In the next release we have new feature “Sending usage statistics” in Fuel: https://blueprints.launchpad.net/openstack/?searchtext=send-anon-usage

We should create automatic system tests for that feature which can be executed on CI in daily basis.

Test integration plan:

 - we should add additional environment variables in tests settings which will be used for enabling of stats collecting/sending and defining collector IP address;
 - add methods which enable/disable collecting of statistics in tests and can force sending of data to collector;
 - add separate test (or maybe decorator) which can use environment snapshots created by other tests (or last created environment), checks that appropriate common logs (cluster creation/configuring, roles definition, deployment result) were added to Nailgun’s database (action_logs), sent to the collector (parse stats sender logs) and correctly saved there (ssh to test VM with collector and check DB). For separate test we can use predefined test scenario of environment snapshots which is reverted or parse scenario from doc string in case of decorator.
- check stat sending with enabled/disabled setting
- check saved content in the Nailgun DB action_logs. saved content should not contain any passwords, ips, netmasks, emails, tenants, session ids
- check sending statistics into collector:
    - send action logs of all types
    - check only not sent before action logs are sent
    - send installation structure in ha and multinode modes
- check data in the collector DB:
    - check no passwords, ips, netmasks, emails, tenants, session ids in action_logs, installation_structures tables
- check migration from collector DB into Elasticsearch
    - check modified installation structs migration
    - check only new action_logs migration