Improve rust/cargo support by:
1) Better handling only toplevel Cargo configuration files for dependency
lookup.
2) Adding runtime requirements for buildreq packages in order to get
dependencies from non directly dependent packages resolved.
3) Add cargo as a buildreq for rust packages to handle the rustc/cargo
split.
4) Add cargo detection from failed_commands.
5) Fix rust source directory destination to not append version in case
the package name already had version information in it.
6) Get name and version information from crates.io package files.
Minor clean up of buildreq module, including the following changes:
- Remove unused import "tarball"
- Add function docstrings
- Convert to list-driven pattern checks instead of a long list of
conditionals.
- Rename variable names that were overriding keywords (file, buffer,
etc.)
- Remove unused setup_py_python3 function
- Remove unused arguments and variables from scan_for_configure function
(and corresponding function calls in test_buildreq.py and autospec.py)
Most changes made at pylint and pycodestyle suggestions.
Shortcomings were identified in setup.py parsing for python build
requirements. These tests more exhaustively test the cases we have been
seeing in the wild.
This patch makes some simplifications to the buildreq module and related
modules (autospec and config). These are mostly readability changes and
code cleanup.
William Douglas