[RFE] boolean conversion should test for 'False'

[Daniel Messer]

Currently string-to-boolean conversion is implemented with testing the supplied string case-insensitive for "true". The same should exist for "false". When used and/or called by YAML-based front-end tools overriding this parameter from true to false will be cryptic, e.g.

---
private: ''

When boolean conversion recognizes input as typically obtained from JSON or YAML input it could be written more clearly:

---
private: 'False'

Background: my current use case for this is in Ansible Tower using OpenStack Dynamic Inventories.