max.hirschhorn@10gen.com located this in a patch build:

https://evergreen.mongodb.com/task/mongodb_mongo_master_linux_64_2518e60c495a700cbb44237425ecf064db970dbd_15_05_15_19_37_32_multiversion_linux_64

it is a consequence of mongorestore's parallel restore triggering multiple collections being created at once, each needing to get the database lock on the server side but only one.
Unclear if this should be implemented as a fix in the tool itself to serialize collection creation to avoid this, or improve the lock handling in the server (increase timeout?) to prevent the error