library: Rename invocation return value
library: Rename invocation return value

Since `invocation` is an Ansible special value that is set for
triple verbosity, it is now visible for smaller verbosity. Therefore
rename it to `_invocation`, which seems to work with less verbosity.
Also adjust the content to match the regular `invocation` style.

linux-system-roles/network,linux-system-roles/network,linux-system-roles/network