Refactor test script
Refactor test script

Check for correct arguments, quote variables, ensure exactly one test
file matches the pattern, and print usage information.

emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen