lsfd: use path_cxt to read process

lsfd: use path_cxt to read process

* path_cxt is based on openat-like functions and lib/path.c provides
  large number of utils to use it
* one handler is re-used for all processes to reduce memory allocation
* list of process is moved to lsfd_control to make it available everywhere
* read tasks when we read process, no later
* lists initialization is done when object (process) is allocated

Signed-off-by: Karel Zak <kzak@redhat.com>