Extract Review: Multilayer specification for ffmpeg

[iLLiCiTiT]

Changelog Description

Extract review is specifying layer name when exr is multilayer.

Additional info

This issue was discovered with renders from blender where output exr had channels ['Main.AOV.R', 'Main.AOV.G', 'Main.AOV.B', 'Main.AOV.A', 'Main.Combined.R', 'Main.Combined.G', 'Main.Combined.B', 'Main.Combined.A', 'Main.Normal.X', 'Main.Normal.Y', 'Main.Normal.Z', 'Main.Test.X'] which failed in ffmpeg.

Testing notes:

1. First of all, any other current exr processing should still work (e.g. multipart exrs from maya)
2. Render from blender (testing for @simonebarbieri )

[kalisp]

This doesn't seem to break anything in automatic tests, but I don't think that tests would be actually testing this.

[iLLiCiTiT]

We also want to add option to be able define preferred layer names to be used for review, but that's for another PR.