LUKS: create devices in parallel

[arithx]

Feature Request

Desired Feature

We should handle LUKS device creation in parallel to speed up configuration.

[arithx]

Deferring this issue for now. There isn't a clear way to perform parallel luksFormat without potentially running into an oomkill at the moment (luksOpen has --serialize-memory-hard-pbkdf but that still puts us into a serial workflow) nor are there guaranteed memory limits needed by each process.