ujail: rework fs jail part

ujail: rework fs jail part

Change functions to work with full paths (do less split and concat of path)
  Store "soname" as key and the fullpath as path in "libraries"
  Remove "extras" list and replace it with "mounts" avl_tree
  ("mounts" also store fullpath)

Add add_path_and_deps() function to handle file/lib openning and mmaping
  Check if file is an elf (magic number) before passing it to elf_load_deps()
  elf_load_deps() now only handle elf parsing part
  next commit adds script (#!) handling

Use add_path_and_deps() with -r and -w args to automatically add dependencies

Signed-off-by: Etienne CHAMPETIER <champetier.etienne@gmail.com>