Update validation computation code control-flow

[a-lemus96]

• [x] Change no_val arg to val in order to enable in-training validation computation
• [x] Update control flow accordingly in runfile
• [x] Update the number of input views for validation computation

Update validation computation code. It should work with the following command structure

parameters:
  scene:
    values: [fern, fortress, flower, room]
  ao:
    values: [1e-7, 1e-6, 1e-5]
  n_imgs:
    values: [2, 4]
command:
  - ${env}
  - ${interpreter}
  - ${program}
  - --n_iters
  - 50000
  - --dataset
  - llff
  - --scheduler
  - exp
  - ${args}

Originally posted by @a-lemus96 in #77