Added test for abstract shard key
Added test for abstract shard key

cogniteev/mongoengine,iandd0824/mongoengine,MakerReduxCorp/mongoengine,depop/mongoengine-stripped,touilleMan/mongoengine,noirbizarre/mongoengine,ConsumerPhysics/mongoengine,DavidBord/mongoengine,cogniteev/mongoengine,elephanter/mongoengine,starsirius/mongoengine,khallaghi/mongoengine,gavincabbage/mongoengine,ProgressivePlanning/mongoengine,Catstyle/mongoengine,WingGao/mongoengine,Multiposting/mongoengine,nicolascine/mongoengine,prijindal/mongoengine,closeio/mongoengine,reallistic/mongoengine,hmarr/mongoengine,MongoEngine/mongoengine,nathanial/mongoengine,jimmyshen/mongoengine,MRigal/mongoengine,losintikfos/mongoengine,eli-b/mongoengine,larsbutler/mongoengine,muhammad-ammar/mongoengine,sourcelair/mongoengine,gmacon/mongoengine,Davidrjx/mongoengine,blaggacao/mongoengine,9nix00/mongoengine,RussellLuo/mongoengine,Davidrjx/mongoengine,yarneo/mongoengine,MakerReduxCorp/mongoengine,ms5/mongoengine