Changes include:

 * Update Makefile to use credentials.yml when it exists
 * Add details on the use of the credentials.yml file to README.md.
 * Update credentials.template comments

Also, fixed a bug where the tags were being merged into the wrong
data structure (passed_vars) in _build_role_dependencies()

Fixes #6439
Fixes #5709

Fix for hostkey directory

Remove dependency on pycurl in apt_repository

Pass through vault_password when parsing host/group vars as directories.

Add space after full stop in ansible-galaxy help

adding -K flag for ask-sudo-pass to ansible-pull

Fixes #6517

Fixes #6471

The `apt` and `yum` modules will automatically install python dependencies.
This change updates the existing integration tests to test whether auto-install
of dependencies is functioning properly.

fetch_url: Avoid credential stripping for FTP-scheme URLs

fix: bug in apt module when python-apt is not available

Fixes a bug where vault_password parameter was not passed through in
_load_vars_from_folder()

modified:   lib/ansible/inventory/vars_plugins/group_vars.py

Allow = symbols in variable values in host inventory

Fix idempotence in mongodb_user module