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 ee9a0f056e445adea2c5e5f150cd51adbb765dab)