MM-10020: avoid duplicating unique indexes (#8587)

* unit test TestGet(Search)Replica

This adds partial, testing-focused support for SQLite, as well as removing
some translated log messages that required initializing i18n just for
testing.

* avoid returning master twice when no replicas are configured

* remove duplicate indexes

* unit test GetAllConns

model/config.go

@@ -21,6 +21,7 @@ const (
 	IMAGE_DRIVER_LOCAL = "local"
 	IMAGE_DRIVER_S3    = "amazons3"
 
+	DATABASE_DRIVER_SQLITE   = "sqlite3"
 	DATABASE_DRIVER_MYSQL    = "mysql"
 	DATABASE_DRIVER_POSTGRES = "postgres"