Stop packages from accessing internet during installation

[AlexanderRichert-NOAA]

Based on installing spack-stack-1.6.0 on Acorn, I found three packages that access the internet at install time (i.e., can't be completely pre-fetched), which causes the build to hang when building on the Acorn compute nodes. These are proj, cprnc, and py-nbconvert.

• proj - Fix test settings for proj (no googletest) spack#389
• cprnc - Add genf90 resource for cprnc to allow offline builds spack/spack#42015
• py-nbconvert - py-nbconvert: avoid install-time downloads spack/spack#42024

[climbfuji]

Thanks for this @AlexanderRichert-NOAA !

[AlexanderRichert-NOAA]

All done