Replace functions in utils with oslo.fileutils

The following functions have moved to oslo.
ensure_tree
remove_path_on_error
file_open
delete_if_exists

Replaced overlapping functions with the ones in fileutils

Change-Id: Ib10a7ca2c72620f7f1df6c5bd4ef6c9cc4d8e913
Merge "Replace functions in utils with oslo.fileutils"