Incorrect Yang models should not prevent functionality from unrelated components

In Beryllium, all jobs were failing due to Restconf getting stuck in http code 401.
Investigation suggests it is not an AAA bug, it is Yangtools unable to move on when encountering invalid Yang modules.

The situation with all jobs can be solved in integration/distribution by removing offending features; but as ODL grows, it would be good to make the core more resistant to low-quality components.

Search for "Failed to parse YANG from source" in (long) [0] to see current offending projects, see [1] for the integration/distribution fix (which perhaps will be merged as 31720 instead).

[0] https://jenkins.opendaylight.org/releng/view/bgpcep/job/bgpcep-csit-1node-periodic-throughpcep-all-beryllium/83/consoleFull
[1] https://git.opendaylight.org/gerrit/31715