Read absolute path for binary execution for matchBinaries

[mtardy]

This is a followup of #1731.

[For matchBinaries] the binary path is just the arg passed to execve and thus can be a relative path (this explains many of the users issues). A future patch is needed to read the absolute path of the task_struct (as we do on userspace side with /proc to fill the initial state of the execve_map) to make this feature complete.

I agree that this is not tied to this PR but this would be also a great improvement in matchBinaries for a follow-up PR. I believe what you do here will help to have the full binary path ready from the kernel. Maybe we need to create an issue to keep track of this (if we do not already have one).

Originally posted by @tpapagian in #1731 (review)

Might be useful: #90.