tests/functional: replace 'run_cmd' with subprocess helpers

The 'run_cmd' helper is re-implementing a convenient helper that
already exists in the form of the 'run' and 'check_call' methods
provided by 'subprocess'.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20241217155953.3950506-29-berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
6 files changed