Modification on rhoPimpleFoam pEq's for handling rho thermo and incompressible...

Modification on rhoPimpleFoam pEq's for handling rho thermo and incompressible EoS. Adding rho limiters if p is limited.
This is important when LTS stepping or large Co number is used.

Updating rhoBuoyantPimpleFoam to handle closed domain for rho thermo and incompressible Eos.
Consolidating chtMultiRegionSimpleFoam and chtMultiRegionFoam pEqs to use the same formulation as rhoBuoyantPimpleFoam and
rhoBuoyantSimpleFoam