Split Odin-II and VPR into separate containers

[umarcor]

Currently, vtr images build both Odin-II and VPR in a single stage. It would be desirable to have separated "green" images for them, and then combine both to create the vtr "brown" image.

Refs:

• Verilog-to-Routing #38
• Actually build the Dockerfile on CI verilog-to-routing/vtr-verilog-to-routing#1756