add empty keepers checking in ibc NewKeeper (backport cosmos#1284) (c…

…osmos#1382)

* add empty keepers checking in ibc NewKeeper (cosmos#1284)

* add empty keepers checking in ibc NewKeeper

* check for empty exported keepers instead of empty sdk-defined keeper structs

* Update modules/core/keeper/keeper.go

Co-authored-by: colin axnér <25233464+colin-axner@users.noreply.github.com>

* remove func checkEmptyKeepers(), check empty keepers directly within func NewKeeper()

* modules/core/keeper KeeperTestSuite -> MsgServerTestSuite; creat new modules/core/keeper KeeperTestSuite for testing ibckeeper.NewKeeper()

* update CHANGELOG.md

* DummyStakingKeeper -> MockStakingKeeper

* refactor modules/core/keeper test

* Update modules/core/keeper/keeper_test.go

Co-authored-by: colin axnér <25233464+colin-axner@users.noreply.github.com>

* Update modules/core/keeper/keeper.go

Co-authored-by: colin axnér <25233464+colin-axner@users.noreply.github.com>

Co-authored-by: colin axnér <25233464+colin-axner@users.noreply.github.com>
(cherry picked from commit f2577f9)

* fix conflict

* fix conflict

Co-authored-by: khanh <50263489+catShaark@users.noreply.github.com>
Co-authored-by: crodriguezvega <carlos@interchain.io>