Run functional tests in parallel

• Run functional tests with multiple jobs, currently 4
• Remove some code duplication in test code

Each test runs on its own copy of database. After the test completes the database is deleted. It is not deleted when test fails. This reduces tests run time on CI from ~320s to ~180s

• Should we use uuidgen tool instead of reading from /proc to generate UUID? This requires updating docker images used to build the project UUIDs are so longer used.
• Examples tests prepare virtual environment. Currently it is shared for all tests. After this change it is recreated for each test and then deleted Fixed, venvs are no longer recreated every time.