manager.c: Restrict ModuleLoad to the configured modules directory.

manager.c: Restrict ModuleLoad to the configured modules directory.

When using the ModuleLoad AMI action, it was possible to traverse
upwards through the directories to files outside of the configured
modules directory. We decided it would be best to restrict access to
modules exclusively in the configured directory. You will now get an
error when the specified module is outside of this limitation.

Fixes: #897
UserNote: The ModuleLoad AMI action now restricts modules to the
configured modules directory.

(cherry picked from commit 5a237235c00a3a408ddb65874f39dab76f3824cf)