Implement clean-path

We shouldn't give non-clean paths to tools -- if a/b/../file was
specified, we can simplify that path to a/file, and not need to create
a/b just to make the path name work.

The testcases come from golang's filepath.Clean tests, this should be
compatible with that implementation.

Bug: 37716307
Test: TEST_MAKE_clean_path=true m -j blueprint_tools
Change-Id: I290a02b0a1e4a7c2b9255bca3c881589b521c402