select/cray: support for passing Accelerator parameters

With regard to forthcoming Accelerator support in Basil 1.2/Alps 4.0, this adds
interface support for passing the following Accelerator parameters:
 * accelerator type (currently only "GPU" is supported),
 * model/rank information (uninterpreted "family" string),
 * amount of on-board memory in MB.
02_Cray-Accelerator-params.diff
Patch from Gerrit Renker and Stephen Trofinoff, CSCS.