environment: add a sleep after starting firewalld service
this is required to avoid hanging of firewall-cmd: a combination of start/restart/stop of firewalld service with the "right" timing could cause the service to hang. This would cause many test failures due to test timeout:
- no_error_when_firewald_restarted
- show_zones_after_firewalld_install
- connectivity_check
- disable_connectivity_check
- ... and other failures as NM will try to contact firewalld during connection activations and will wait 10 seconds for firewalld before giving up and proceding in the connection activation: in many tests a delay of 10 seconds while connection activation is too much, triggering the test failure. Some affected tests:
- snapshot_rollback
- snapshot_rollback_all_devices
- snapshot_rollback_all_devices_with_timeout
- snapshot_rollback_soft_device
- alias_ifcfg_reboo- ...