Make some of the optional requirements optional for testing -- we'll skip the tests instead

Prefer dnf to yum.

On Fedora 22 and later, yum is deprecated and dnf is installed by
default. However, the detection do not seems to take this in account,
and always use yum, even when yum cli is just a wrapper to tell "use
dnf", as this is the case on F22 and later ( see package dnf-yum ).

As dnf is not installed by default, except on F22, this shouldn't
break anything.

Vagrant inventory: exit 0 on success

Use abc for BaseCacheModule

Remove old dead code ( variable no longer exist, not used )

Fix errors reporting for playbook/*

Do add a unused named argument using a variable that was removed

Fix serialize function by using the right members name

Fix variable name

problem that the update fixes:

https://github.com/ansible/ansible-modules-core/issues/1064

Found by pylint.

There is no 'role' variable, and given the test and code after, that's
likely a test on 'ds'

Fix the filename in error message (pylint)

Fix various pylint issues ( missing import and wrong variable names )

Fix the name of the exported class ( pylint )

fixed indent when looking at delegate_to vars

(We have a jenkins build that creates a [testenv:jenkins] so it needs
there to be a default value

Rename the import, since the directory was renamed for v2

Add missing imports. They are used later in mkdtmp, needed by action plu...

Add/correct missing imports for AnsibleError in v2 lookup plugins