Remove _path_exists method.

This method is buggy because it works only on host machine with english language, and
apparently this method is also useless because we don't need to check if a path exist if
we can use command option -p for "mkdir" command and option -f for "rm" command.

bug: LP#1172777
Change-Id: I418b32772ca97b42e1a43275a7abec9f96688607
Merge "Remove _path_exists method."