windows: fix log collection

windows: fix log collection

The "Get-WinEvent" command used to retrieve Windows event log
messages can fail if the specified log has no entries.

We're using the "SilentlyContinue" action to avoid erroring out
in such cases.

However, the script still terminates abruptly while collecting
logs. For this reason, we'll use the "Ignore" error action instead.
We'd rather not have test failures just because we failed to
retrieve some Windows event log entries.

Unlike "SilentlyContinue", "Ignore" doesn't populate the global
$Error variable, which may be used when running the script
remotely.

While at it, we're adding some log messages at the end of the
"run_tests" and "collect-event-logs.ps1" scripts.

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>