relion_run_ctffind defaults to using a single GPU for Gctf, even if more are available

[Oliver Clarke]

Hi Sjors,

If I run Gctf via relion_run_ctffind and don't explicitly specify which GPUs to use, it defaults to using just the first one. I think it probably should use all GPUs available if unspecified, to be consistent with the behavior of other relion programs that take the --gpu flag.

Cheers Oli