feat(MCOL-6082) Cluster with read-only nodes should correctly work with DML

This patch changes logic from counting all nodes to counting only
read-write nodes when messaging about DML operations.

feat(MCOL-6082): Multiple readers of dbroots using OamCache logic

This patch introduces centralized logic of selecting what dbroot is
accessible in PrimProc on what node. The logic is in OamCache for time
being and can be moved later.

Fix build

writeengine/client/we_ddlcommandclient.h

@@ -26,6 +26,7 @@
 #include "dbrm.h"
 #include "liboamcpp.h"
 #include "writeengine.h"
+#include "oamcache.h"
 
 #define EXPORT
 
@@ -50,7 +51,7 @@ class WE_DDLCommandClient
  private:
   BRM::DBRM fDbrm;
   WEClients* fWEClient;
-  oam::Oam fOam;
+  oam::OamCache* fOamCache;
 };
 
 }  // namespace WriteEngine