dnf_package resource's flush_cache property does not respect :after

[dafyddcrosby]

Description

There is a documented flush_cache property that should allow avoiding use of the in-memory cache after an install/remove action is taken. It looks like the functionality was removed in aebaee1, and we always flush the cache after install

Initially this could be thought to be merely a documentation bug, but there's an interesting use case for avoiding a call to the Python helper, which is when the underlying Chef Infra Client RPM has been changed, and the path to the dnf_helper.py script (in DNF_HELPER is now broken.

So there's two parts to this fix:

1. Update the documentation so that the assumed default for :after is true (ie the current behaviour).
2. Use flushcache if new_resource.flush_cache[:before] == false or something roughly similar in install_package and remove_package methods.

Chef Version

Chef 18.5.0 (this bug goes back to Chef 12.21.3, though)

Platform Version

CentOS