TUT: use general 'scale' instead of 'convertToMeters' in blockMeshDict

- although this has been supported for many years, the tutorials
  continued to use "convertToMeters" entry, which is specific to blockMesh.
  The "scale" is more consistent with other dictionaries.

ENH:
- ignore "scale 0;" (treat as no scaling) for blockMeshDict,
  consistent with use elsewhere.

tutorials/preProcessing/createZeroDirectory/cavity/system/blockMeshDict

@@ -14,7 +14,7 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-convertToMeters 0.1;
+scale   0.1;
 
 vertices
 (

tutorials/preProcessing/createZeroDirectory/motorBike/system/blockMeshDict

@@ -15,7 +15,7 @@ FoamFile
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-convertToMeters 1;
+scale   1;
 
 vertices
 (

tutorials/preProcessing/createZeroDirectory/snappyMultiRegionHeater/system/blockMeshDict

@@ -14,7 +14,7 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-convertToMeters 1;
+scale   1;
 
 vertices
 (