blockMesh: Change default location of blockMeshDict from constant/polyMesh to system

For multi-region cases the default location of blockMeshDict is now system/<region name>

If the blockMeshDict is not found in system then the constant directory
is also checked providing backward-compatibility

tutorials/basic/potentialFoam/cylinder/system/blockMeshDict

@@ -0,0 +1,156 @@
+/*--------------------------------*- C++ -*----------------------------------*\
+| =========                 |                                                 |
+| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
+|  \\    /   O peration     | Version:  dev                                   |
+|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
+|    \\/     M anipulation  |                                                 |
+\*---------------------------------------------------------------------------*/
+FoamFile
+{
+    version     2.0;
+    format      ascii;
+    class       dictionary;
+    object      blockMeshDict;
+}
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+convertToMeters 1;
+
+vertices #codeStream
+{
+    codeInclude
+    #{
+        #include "pointField.H"
+    #};
+
+    code
+    #{
+        pointField points(19);
+        points[0]  = point(0.5, 0, -0.5);
+        points[1]  = point(1, 0, -0.5);
+        points[2]  = point(2, 0, -0.5);
+        points[3]  = point(2, 0.707107, -0.5);
+        points[4]  = point(0.707107, 0.707107, -0.5);
+        points[5]  = point(0.353553, 0.353553, -0.5);
+        points[6]  = point(2, 2, -0.5);
+        points[7]  = point(0.707107, 2, -0.5);
+        points[8]  = point(0, 2, -0.5);
+        points[9]  = point(0, 1, -0.5);
+        points[10] = point(0, 0.5, -0.5);
+        points[11] = point(-0.5, 0, -0.5);
+        points[12] = point(-1, 0, -0.5);
+        points[13] = point(-2, 0, -0.5);
+        points[14] = point(-2, 0.707107, -0.5);
+        points[15] = point(-0.707107, 0.707107, -0.5);
+        points[16] = point(-0.353553, 0.353553, -0.5);
+        points[17] = point(-2, 2, -0.5);
+        points[18] = point(-0.707107, 2, -0.5);
+
+        // Duplicate z points
+        label sz = points.size();
+        points.setSize(2*sz);
+        for (label i = 0; i < sz; i++)
+        {
+            const point& pt = points[i];
+            points[i+sz] = point(pt.x(), pt.y(), -pt.z());
+        }
+
+        os  << points;
+    #};
+};
+
+
+blocks
+(
+    hex (5 4 9 10 24 23 28 29) (10 10 1) simpleGrading (1 1 1)
+    hex (0 1 4 5 19 20 23 24) (10 10 1) simpleGrading (1 1 1)
+    hex (1 2 3 4 20 21 22 23) (20 10 1) simpleGrading (1 1 1)
+    hex (4 3 6 7 23 22 25 26) (20 20 1) simpleGrading (1 1 1)
+    hex (9 4 7 8 28 23 26 27) (10 20 1) simpleGrading (1 1 1)
+    hex (15 16 10 9 34 35 29 28) (10 10 1) simpleGrading (1 1 1)
+    hex (12 11 16 15 31 30 35 34) (10 10 1) simpleGrading (1 1 1)
+    hex (13 12 15 14 32 31 34 33) (20 10 1) simpleGrading (1 1 1)
+    hex (14 15 18 17 33 34 37 36) (20 20 1) simpleGrading (1 1 1)
+    hex (15 9 8 18 34 28 27 37) (10 20 1) simpleGrading (1 1 1)
+);
+
+edges
+(
+    arc 0 5 (0.469846 0.17101 -0.5)
+    arc 5 10 (0.17101 0.469846 -0.5)
+    arc 1 4 (0.939693 0.34202 -0.5)
+    arc 4 9 (0.34202 0.939693 -0.5)
+    arc 19 24 (0.469846 0.17101 0.5)
+    arc 24 29 (0.17101 0.469846 0.5)
+    arc 20 23 (0.939693 0.34202 0.5)
+    arc 23 28 (0.34202 0.939693 0.5)
+    arc 11 16 (-0.469846 0.17101 -0.5)
+    arc 16 10 (-0.17101 0.469846 -0.5)
+    arc 12 15 (-0.939693 0.34202 -0.5)
+    arc 15 9 (-0.34202 0.939693 -0.5)
+    arc 30 35 (-0.469846 0.17101 0.5)
+    arc 35 29 (-0.17101 0.469846 0.5)
+    arc 31 34 (-0.939693 0.34202 0.5)
+    arc 34 28 (-0.34202 0.939693 0.5)
+);
+
+boundary
+(
+    down
+    {
+        type symmetryPlane;
+        faces
+        (
+            (0 1 20 19)
+            (1 2 21 20)
+            (12 11 30 31)
+            (13 12 31 32)
+        );
+    }
+    right
+    {
+        type patch;
+        faces
+        (
+            (2 3 22 21)
+            (3 6 25 22)
+        );
+    }
+    up
+    {
+        type symmetryPlane;
+        faces
+        (
+            (7 8 27 26)
+            (6 7 26 25)
+            (8 18 37 27)
+            (18 17 36 37)
+        );
+    }
+    left
+    {
+        type patch;
+        faces
+        (
+            (14 13 32 33)
+            (17 14 33 36)
+        );
+    }
+    cylinder
+    {
+        type symmetry;
+        faces
+        (
+            (10 5 24 29)
+            (5 0 19 24)
+            (16 10 29 35)
+            (11 16 35 30)
+        );
+    }
+);
+
+mergePatchPairs
+(
+);
+
+// ************************************************************************* //