inspection: improve package info error message

[abn]

A common issue when determining root cause of inspection errors is the lack of information on why a package inspect failed (eg: #2898). This change improves the situation by adding more contextual information for failures.

Current error output

$ poetry@master add git+https://bitbucket.org/jmtaylor/py_sad_correlation

  PackageInfoError

  Unable to determine package info for path: /tmp/pypoetry-git-py_sad_correlationaw_3sjs8

  at ~/.local/pipx/venvs/poetry@master/lib64/python3.8/site-packages/poetry/inspection/info.py:485 in _pep517_metadata
      481│                 try:
      482│                     venv.run("python", "setup.py", "egg_info")
      483│                     return cls.from_metadata(path)
      484│                 except EnvCommandError:
    → 485│                     raise PackageInfoError(path)
      486│                 finally:
      487│                     os.chdir(cwd.as_posix())
      488│ 
      489│         if info:

New error output

$ poetry@local add git+https://bitbucket.org/jmtaylor/py_sad_correlation

  PackageInfoError

  Unable to determine package info for path: /tmp/pypoetry-git-py_sad_correlations74oa0g7
  
  Fallback egg_info generation failed.
  
  Command ['/tmp/tmptlla0klg/.venv/bin/python', 'setup.py', 'egg_info'] errored with the following return code 1, and output: 
  Traceback (most recent call last):
    File "setup.py", line 2, in <module>
      import numpy  # So we can work out where the numpy headers live!
  ModuleNotFoundError: No module named 'numpy'

  at ~/workspace/python-poetry/poetry/poetry/inspection/info.py:484 in _pep517_metadata
      480│                 try:
      481│                     venv.run("python", "setup.py", "egg_info")
      482│                     return cls.from_metadata(path)
      483│                 except EnvCommandError as fbe:
    → 484│                     raise PackageInfoError(path, "Fallback egg_info generation failed.", fbe)
      485│                 finally:
      486│                     os.chdir(cwd.as_posix())
      487│ 
      488│         if info:

[github-actions]

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