Update most SR tests to use slapos.testing

Update almost all tests to use https://lab.nexedi.com/nexedi/slapos.core/merge_requests/64

Notable changes:

• the testcase class is generated dynamically with makeModuleSetUpAndTestCaseClass
• self.slap allow low level control of slapos
• IP addresses are available as _ipv6_address and _ipv4_address class attributes
• getSupervisorRPCServer no longer exist, instead use self.slap.instance_supervisor_rpc (as context manager)
• now the framework takes care of running promises and instance step fail when instanciation fail or when promises are not satisfied (as a result, some tests checking promises are dropped)
• test needs slapos and supervisord commands in PATH. It's important to have a recent enough slapos and not the ~/bin/slapos from slaprunner which sets $SLAPOS_CONFIGURATION

Following tests were not updated:

• caddy-frontend as this will require more work, because this software uses shared partitions and maybe other things will need to be adapted in the tests.
• slapos-master as it is same as ERP5 and I thought maybe we can do better than duplicating code, so I left it as is for now.
• nextcloud as this fail the slapos node instance step.

There are also a few style changes or small fixes to make pylint happy and some other fixes for problems with softwares and also a fix for seleniumrunner flaky test.