[WIP] OXT-1736 : do-build.sh zeus uprev and usability improvements

[stacktrust]

This is a collection of usability improvements for the non-container build script. This is a precursor to adding support for OE multiconfig builds.

• Check for bash on systems (e.g. Devuan) where default shell is not bash
• Regenerate local.conf (with version strings) for every build
• Create symlink to most recent build, useful for PXE boot package repo.
• Enable "interactive" mode to skip log collection and use non-scrolling bitbake status
• Enable memory-resident bitbake with short timeout for multiple bb invocations.
• Example config: pyro -> zeus7, bitbake 1.34 -> bitbake 1.44
• Remove unused code, initialize undefined variables

OXT-1736