Fix api_paste_config typo in cinder.conf.erb

Cinder config template.conf.erb has typo which causes api-paste.ini to be ignored.

- Change api_paste_confg to api_paste_config in cinder.conf.erb
  template

  See rcbops/chef-cookbooks#900

(cherry picked from commit 37cfee8248a9b2e60c5537f827e83ed12e392db2)