ENH: linear solvers: add variable-specific debug flags

Summary

• a762a311 - ENH: linear solvers: add variable-specific debug flags
• 390e7b0a - TUT: rotatingFanInRoom: perturb locationInMesh (fixes #2162 (closed))
• 7d7e012e - ENH: KirchhoffShell: simplification of log output

Introduces a new optional keyword of label type 'log' to linear-solver dictionaries to enable variable-specific debug statements. For example, in fvOptions file:

solvers
{
    p
    {
        solver GAMG;
        ...
        log    2;
    }

    U
    {
        ...
        log    0;
    }
}

The meanings of values of 'log' are:

log    0;    <!--  no output
log    1;    <!--  standard output
log    2;    <!--  debug output
// values higher than 2 are expected to have no effect

Resolved bugs (If applicable)

#2162 (closed)

EP#1615 @Chiara

Risks

This keyword does not directly affect the operations of various DebugSwitches and backward compatibility has been ensured in exchange of code cleanness. The related DebugSwitches are:

DebugSwitches
{
    SolverPerformance    0;
    GAMG                 0;
    PCG                  0;
    PBiCG                0;
    smoothSolver         0;
}

Test cases

4-ep-1615-solver-verbosity