Fix python-ironicclient crash

- ca_file, cert_file and key_file arguements were renamed part of
  e3d35647 but the commit e3d35647 never renamed the other place this
  variables were used.
- This commit properly renames those variables back to sane values and
  fixes the crash

Change-Id: I7b40b2e6a314abc734d28b76626f09f3d31c0d8b
Closes-Bug: 1386454