Invalid RESOURCE_EXHAUSTED code in spec for CreateSnapshot

[jfbus]

What happened:

The CreateSnapshot spec requires to return a "13 RESOURCE_EXHAUSTED" error:

Not enough space to create snapshot	13 RESOURCE_EXHAUSTED	There is not enough space on the storage system to handle the create snapshot request.

What you expected to happen:

The code for RESOURCE_EXHAUSTED should be 8.

Anything else we need to know?:

Environment:

• CSI Spec version: master
• Others:

[nixpanic]

Looks like PR #578 has been created for this already.