Merge fixes for post layout netlist/sdf generation for blackbox modules

[tpagarani]

Motivate of the pull request

• To address an existing issue. If so, please provide a link to the issue:
• Breaking new feature. If so, please describe details in the description part.

Describe the technical details

What is currently done? (Provide issue link if applicable)

What does this pull request change?

Which part of the code base require a change

• VPR
• Tileable routing architecture generator
• OpenFPGA libraries
• FPGA-Verilog
• FPGA-Bitstream
• FPGA-SDC
• FPGA-SPICE
• Flow scripts
• Architecture library
• Cell library
• Documentation
• Regression tests
• Continous Integration (CI) scripts

Impact of the pull request

• Require a change on Quality of Results (QoR)
• Break back-compatibility. If so, please list who may be influenced.

[tangxifan]

LGTM. But I will upgrade the VPR version in OpenFPGA very soon. We will have better VPR (PnR results).