[BOOT:BOOTMGR] Begin work on BCD support

Added stub for BmOpenDataStore()

BOOT/ENVIRON/APP/BOOTMGR/bootmgr.c

@@ -41,6 +41,7 @@ Return Value:
 {
     NTSTATUS Status;
     BOOT_LIBRARY_PARAMETERS LibraryParameters;
+    HANDLE DataStore;
 
     LibraryParameters.Flags = 0;
 
@@ -53,6 +54,11 @@ Return Value:
         goto Exit;
     }
 
+    //
+    // Open the boot data store.
+    //
+    (VOID)BmOpenDataStore(&DataStore);
+
 Exit:
     BlDestroyLibrary();
     return Status;