Adapt tests for centos7 environment

[Lagovas]

Here are several updates to simplify running tests on centos 7/8 which uses python 3.6.8. Replaces shutil to simplified version and used pre-compiled psycopg2 due to problems with postgresql-devel packages on centos and building pyscopg2 from sources. For us no difference in where to get psycopg2 for tests.

Checklist

• [ ] Change is covered by automated tests
• [ ] The coding guidelines are followed
• [ ] Public API has proper documentation in the Acra documentation site or has PR on documentation repository with new changes
• [ ] CHANGELOG.md is updated (in case of notable or breaking changes)
• [ ] CHANGELOG_DEV.md is updated
• [ ] Benchmark results are attached (if applicable)
• are up-to-date (in case of API changes)