Backend plugin system (#2874)

* Add backend plugin changes

* Fix totp backend plugin tests

* Fix logical/plugin InvalidateKey test

* Fix plugin catalog CRUD test, fix NoopBackend

* Clean up commented code block

* Fix system backend mount test

* Set plugin_name to omitempty, fix handleMountTable config parsing

* Clean up comments, keep shim connections alive until cleanup

* Include pluginClient, disallow LookupPlugin call from within a plugin

* Add wrapper around backendPluginClient for proper cleanup

* Add logger shim tests

* Add logger, storage, and system shim tests

* Use pointer receivers for system view shim

* Use plugin name if no path is provided on mount

* Enable plugins for auth backends

* Add backend type attribute, move builtin/plugin/package

* Fix merge conflict

* Fix missing plugin name in mount config

* Add integration tests on enabling auth backend plugins

* Remove dependency cycle on mock-plugin

* Add passthrough backend plugin, use logical.BackendType to determine lease generation

* Remove vault package dependency on passthrough package

* Add basic impl test for passthrough plugin

* Incorporate feedback; set b.backend after shims creation on backendPluginServer

* Fix totp plugin test

* Add plugin backends docs

* Fix tests

* Fix builtin/plugin tests

* Remove flatten from PluginRunner fields

* Move mock plugin to logical/plugin, remove totp and passthrough plugins

* Move pluginMap into newPluginClient

* Do not create storage RPC connection on HandleRequest and HandleExistenceCheck

* Change shim logger's Fatal to no-op

* Change BackendType to uint32, match UX backend types

* Change framework.Backend Setup signature

* Add Setup func to logical.Backend interface

* Move OptionallyEnableMlock call into plugin.Serve, update docs and comments

* Remove commented var in plugin package

* RegisterLicense on logical.Backend interface (#3017)

* Add RegisterLicense to logical.Backend interface

* Update RegisterLicense to use callback func on framework.Backend

* Refactor framework.Backend.RegisterLicense

* plugin: Prevent plugin.SystemViewClient.ResponseWrapData from getting JWTs

* plugin: Revert BackendType to remove TypePassthrough and related references

* Fix typo in plugin backends docs

builtin/credential/aws/backend.go

@@ -17,7 +17,10 @@ func Factory(conf *logical.BackendConfig) (logical.Backend, error) {
 	if err != nil {
 		return nil, err
 	}
-	return b.Setup(conf)
+	if err := b.Setup(conf); err != nil {
+		return nil, err
+	}
+	return b, nil
 }
 
 type backend struct {