[Plasma] Methods in plasma/store.h returning PlasmaError should return Status instead

[asfimport]

These functions are not able to return other kinds of errors (e.g. CUDA-related errors) as a result of this. I encountered this while working on ARROW-2883

Reporter: Wes McKinney / @wesm

_{Note: This issue was originally created as ARROW-2887. Please see the migration documentation for further details.}