gres/gpu: Don't log init() and fini() function runs with info()

This results in the srun command logging the plugin load when gres/gpu
is used, which the user will not want to see.
Introduced in commit 9f9b3407603a58d69ace677d39f4ce8579a8ebb2
GRES accounting data wrong in database

gres_alloc, gres_req, and gres_used fields were empty if the
job was not started immediately.
bug 380
Merge branch 'slurm-2.6'