Fix building in alternative contexts

[ianpittwood]

• Fixes build errors in alternate contexts when using relative paths.
  • Handle any global context as an absolute path by using resolve() against it.
  • Use resolve() against BakePlan.bake_file to ensure relative paths are not misrepresented due to change in working directory.
• Present tracebacks on exceptions unrelated directly to an image build.
• Replace any other usages of absolute() with resolve() to ensure symlinks can be handled correctly.

[github-actions]

Test Results

733 tests   733 ✅  2m 40s ⏱️
  1 suites    0 💤
  1 files      0 ❌

Results for commit d9524fd.