pcap: Fix a test so that it works in any time zone

Change-Id: I79d1cff9cb6be30c73ec0d5c4ba05d682b919202
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/35081
Tested-by: Hudson CI
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>