Use virtualenv 20.0.10 for macosx tests

[Ch3LL]

What does this PR do?

Running into this issue on mac tests: pypa/virtualenv#1581

There is a test that removes pip, and because of this issue with subproccess and virtualenv it uses the incorrect path and ends up removing the pip binary in the nox virtual environment and not the one created during the test run. This is fixed on mac with virtualenv version 20.0.10 hence upgrading the version here. Also had to make some updates to ensure the tests work with this new version.

This will fix the failing tests:

    integration.modules.test_pip.PipModuleTest.test_chained_requirements__non_absolute_file_path
    integration.modules.test_pip.PipModuleTest.test_issue_4805_nested_requirements
    integration.modules.test_pip.PipModuleTest.test_pip_install_multiple_editables_and_pkgs
    integration.modules.test_pip.PipModuleTest.test_requirements_as_list__non_absolute_file_path
    integration.modules.test_pip.PipModuleTest.test_requirements_as_list_of_chains__cwd_not_set__absolute_file_path
    integration.modules.test_pip.PipModuleTest.test_requirements_as_list_of_chains__cwd_set__absolute_file_path
    integration.modules.test_virtualenv_mod.VirtualenvModuleTest.test_create_defaults
    integration.modules.test_virtualenv_mod.VirtualenvModuleTest.test_site_packages
    integration.states.test_pip_state.PipStateTest.test_issue_2028_pip_installed_state
    integration.states.test_pip_state.PipStateTest.test_issue_2087_missing_pip
    integration.states.test_pip_state.PipStateTest.test_issue_6833_pip_upgrade_pip
    integration.states.test_pip_state.PipStateTest.test_pip_installed_errors
    integration.states.test_pip_state.PipStateTest.test_pip_installed_removed_venv
    integration.states.test_pip_state.PipStateTest.test_pip_installed_specific_env
    unit.states.test_pip_state.PipStateTest.test_install_requirements_parsing
    setUpClass (unit.modules.test_zcbuildout.BuildoutOnlineTestCase)
    setUpClass (unit.modules.test_zcbuildout.BuildoutTestCase)
    setUpClass (unit.states.test_zcbuildout.BuildoutTestCase)

What issues does this PR fix or reference?

#56342