construct faMesh fails with distributed roots

Noticed during testing of #2523 (closed) - needs more attention

Running checkFaMesh with distributed roots:

[0] --> FOAM FATAL ERROR: (openfoam-2206)
[0] Cannot find file "faceLabels" in directory "faMesh" in times "0" down to constant
[0] 
[0]     From virtual Foam::IOobject Foam::fileOperation::findInstance(const Foam::IOobject &, const Foam::scalar, const Foam::word &) const
[0]     in file global/fileOperations/fileOperation/fileOperation.C at line 1139