Fix depth buffering for camera-based observations

[JVillella]

Fix,

# XXX: Though we don't need the depth buffer returned, setting this to 0
#      causes undefined behaviour where the ordering of meshes is random.
fb_props.setDepthBits(1)

Previously sometimes the vehicles would be underneath the map causing the smarts/core/test_observations to fail.

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I also pinned RLlib which was defaulting to install 1.0 which our examples don't presently support.

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Added instructions for running Envision in Docker.

[Gamenot]

If observations fail again the same way we should update the buffer to 8 bit.