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
Add node-set-maintenance command

This command accepts an optional reason and calls the new
/nodes/uuid/maintenance endpoint to set and clear maintenance
mode and maintenance reason.

It will reject setting maintenance mode to off with a reason,
as setting maintenance mode to off clears the reason.

Change-Id: I04e14bc239b343d8791747963e4feec1e2cbdda8
Implements: blueprint maintenance-reason
Merge "Add node-set-maintenance command"