Correct documentation for QualifyingElement options

Add missing `element_` portion of configuration options for
`QualifyingElement`.

Change-Id: I6948ad1a2b0496414159785280d525868202f0f0
Reviewed-on: http://gerrit.causes.com/44371
Reviewed-by: Joe Lencioni <joe.lencioni@brigade.com>
Tested-by: jenkins <jenkins@brigade.com>