fix adobe connect conferences for groups. fixes #CNVS-2483

test plan:
  * configure adobe connect;
  * inside of a course, create a group;
  * as a member of the group, create a group conference;
  * attempt to join the conference and verify that you are
    able to join successfully.

Change-Id: I6d965b502cd6a2bac0b9921235644c04c4ada6f5
properly handle meeting folder errors.

Change-Id: Ic6cbd82c002bf62f746403bc1407b65df115491e
replace `require` calls with `require_relative`.

Change-Id: I28a462ce8409d1e948d9bac5c4bf0ce6209ab96d
use canvas email as username; improve error messaging.

some adobe connect instances require an email address
to be used as a login, so that's how we roll.

also add some additional info to error messaging to
help w/ debugging.

Change-Id: I37f91ffffa2a6b15eb0241be5c7762379d3b9142