ugtrain: split run_shell_cmd() from proc_to_pid()
ugtrain: run the preloader with '-P' option

We can do the following now:
$ ugtrain -P libmemhack64.so chromium-bsu64

This calls the preloader internally with:
$ ugpreload libmemhack64.so chromium-bsu

For security reasons '-P' is ignored if called as root.