Run Additional Library tests also with opensource account

See if there is already account for opensource + additional libraries in https://intranet.qt.io/pages/viewpage.action?pageId=1279244. If not ask Jukka Jokiniva to create one.

Modify suites/shared/shared.py: get_account() to return opensource account for add_on job. Add new 'if'/'elif' that checks: "is_opensouce and is_addon()", but note that it needs to be before the 'common' is_opensource() case so that those two does not get mixed. (apparently is_feature.py needs a is_addon() function also).

Add also trigger jobs if needed.

Create first test plans in TestRail manually: open latest enterprise plan -> 'rerun', change the 'ENT' in the name to 'OSS' -> save.