Implement userspace probe location extraction and registration

These functions use run_as commands to extract the offsets in the binary
where the instrumentation should be placed and pass these offsets
to the kernel tracer along with the FD to complete the registration of
userspace probe events using the two-step registration process.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>