This commit extracts the code that marks the item produced by
probe as incomplete to a static function _mark_collected_object_as_incomplete
so that it can be reused in other code later

If a single OVAL object matches more than 10000 items, we will
stop collecting these items and mark the object as incomplete.
This should prevent some situations in which the produced results
are too large and cause memory problems or inability to generate
the HTML report.

This commit adds a simple test that covers a situation when
the probe collects more items than the limit for a single OVAL object.

The `probe_item_collect` function can fail and it can return various
return codes. But, the return codes aren't handled in the caller
function `process_file`. That means the `process_file` continues to
process items even if no other items can be collected due to memory
constraints or other problems. With this commit, we will read the return
code of `probe_item_collect` and react accordingly.

Users can limit the amount of items collected by setting the
`OSCAP_PROBE_MAX_COLLECTED_ITEMS` environment variable.
By default, the amount of items is unlimited.

The behavior alteration we are testing here is not exactly connected to
memory. I'd rather name it like probe_behavior to make the folder a
collection of tests related to these env. vars.