dcp: User ID and Group ID

[NateThornton]

As part of Near Node Flash (NNF) Data Movement implementation, there is the need to specify the User ID and Group ID when running dcp (explained here).

For dcp, this work seems pretty straightforward to add with -U [uid] and -G [gid].

For example dcp -U 1001 -G 1002 file.in file.out

Does this work for everyone? Any other comments before I begin?

[bdevcich]

I created PR for this: https://github.com/hpc/mpifileutils/pull/540.