dev-container: Add subcommand to run tests

This MR has three related commits:

dev-container: Add subcommand to run tests

• Add new subcommand run-tests to the ./container script and the --pytest-args argument to pass additional arguments to the pytest command.
• Runs tests as root.
• Add new parameters to the SSH command:
  • -Y Enable X11 forwarding to be able to run a browser GUI on a container.
  • -C Use traffic compression so the X11 GUI is not laggy.
  • -t Force pseudo-terminal allocation to enable colors on terminal.
  • Use the LogLevel=error option to suppress some warning messages.
• Update module markers in the pytest.ini file.
• Increase the default container disk size to 12G.
• Update HACKING.md to run unit and functional tests.

PROVISION_SCRIPT:

• Explicitly install sshpass as requirement for tests, needed on Debian stable.
• Ensure that geckodriver.log and .pytest_cache/ exist and are others-writable.

Closes #1901 (closed)

Tests performed:

• Run unit tests on stable, testing and unstable containers, no failed tests.
• Run functional tests on stable and testing containers, no regressions.

functional-tests: Fix installation errors in install.sh script

• On Debian 10, pin pytest-bdd version to 3.2.1, this is the latest version that supports pytest 3.10.1.
• Install wheel and pytest-xdist packages from the Debian repos.
• Add git as a dependency for functional tests.
• Fix regexp when getting Gecko version from the Github api, for some reason after colon, sometimes there is a space and sometimes not.

Tests performed on Debian stable, testing and unstable:

• Installing dependencies with the install.sh script succeeds.
• No regressions when running tests.

users: Skip action script tests if LDAP is not set up

• Also, make sure an admin account exists before some tests.

Tests performed:

• The users module test_actions unit tests are skipped if LDAP is not set up.
• The users module unit tests pass if LDAP is set up.