Add better error reporting if setuptools-scm is not installed

[MHendricks]

Restore hard requirement of setuptools-scm, hab was designed to require it.

Checklist

• I have read the CONTRIBUTING.md document
• I formatted my changes with black
• I linted my changes with flake8
• I have added documentation regarding my changes where necessary
• Any pre-existing tests continue to pass
• Additional tests were made covering my changes

Types of Changes

• Bugfix (change that fixes an issue)
• New Feature (change that adds functionality)
• Documentation Update (if none of the other choices apply)

Proposed Changes

Re-adds setuptools_scm as a hard pip requirement. Adds better error reporting if setuptools_scm is not installed, and improves test coverage over distro_version.py.