Assignment to reserved built-in symbol: dir

In file keystone/common/openssl.py,
BaseCertificateConfigure::_make_dirs(), built-in symbol dir was
re-assignment as local vars, it is easily lead to a misunderstanding, so
rename them.
This patch do not modify any functionality.

Change-Id: I70d6bdc9362577b46b3500de49603f296b6b72e1
Merge "Assignment to reserved built-in symbol: dir"