collect-uprobes.service

This change adds some helper scripts for uprobe enabling and
disabling. The trigger_collector.py script checks all enabled
uprobes and disables them if they were hit (and thus, in the
soft-disabled state).

As an optimization, the two kernel patches are added. 0001-*
changes the trace_entry struct to allow more than 65k probes
and makes disable_event a POST_TRIGGER event, which makes
every event leave exactly one line in the trace output file.
0002-* speeds up the process of inserting all uprobes (~160k
events for the Ubuntu 18.04 web server VM) by removing an
O(n) check for uniqueness - in our case, we know that all
events have unique names.

Lastly, the systemd service file hooks up enable_uprobes.py
as early during boot as possible. The uprobes to be enabled
need to reside at /etc/librarytrader/all_triggers. Note that
inserting ~160k uprobes will take around 2 minutes and will
block before reaching sysinit.target.

After the uprobes have been enabled, another systemd service
starts collect_uprobes.py, which scans the trace filesystem
for soft-disabled uprobes and fully disables them, writing
an entry into a log at /etc/librarytrader/collected_uprobes.