Refactor builder scripts to be more standalone

[gaborcsardi]

Things to decide / design:

• how to parameterize them
• redesign the output

Ideally it should be possible to run the scripts from an ordinary (non R-hub) computer.

[gaborcsardi]

Re parameterization, they take the following arguments currently:

• package (e.g. dotenv_1.0.2.tar.gz)
• filename (on the web app, the random file name, e.g. 73f50bcc11c94566b64963dad0257a3d)
• url (to download it from, internal URL, e.g. http://frontend:3000/file/73f50bcc11c94566b64963dad0257a3d)
• image (for Linux only, e.g. debian-gcc-devel)
• checkArgs (e.g. --as-cran)
• envVars (e.g. _R_CHECK_CRAN_INCOMING_USE_ASPELL_=true) Seems to be newline separated?
• startPingUrl (http://frontend:3000/build/in-progress/dotenv_1.0.2.tar.gz-b90a9e46c9134442974ca74446bff4e7)
• endPingUrl (e.g. http://frontend:3000/build)
• build (logical, whether to run R CMD build)
• pkgname (e.g. dotenv)
• rversion (e.g. r-devel), only for Windows, currently. Linux images have a single version, and macOS builder also.

[gaborcsardi]

So for Linux, we can have these args:

• package file (can also be an url)
• optional docker image
• optional check args
• optional env vars