Allow hacking/env-setup module path to use config file library path

hacking/env-setup now adds the configured library path in ANSIBLE_CONFIG
to the ANSIBLE_LIBRARY environment variable in addition to the previous
default of ANSIBLE_HOME/library.

This replaces #5950.
Merge pull request #5967 from willthames/env_setup_library

Allow hacking/env-setup module path to use config file library path