Auto merge of #761 - tmfink:script-fix, r=fitzgen

Refactor test script

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

Here are some examples:

~~~
$ ./tests/test-one.sh
Usage: ./tests/test-one.sh <fuzzy-name>
~~~

~~~
$ ./tests/test-one.sh zzz
ERROR: no files found with pattern "zzz"
~~~

~~~
$ ./tests/test-one.sh union
ERROR: Expected exactly 1 result, got 15:
./tests/headers/struct_with_anon_unnamed_union.h
./tests/headers/union_dtor.hpp
./tests/headers/union_with_anon_union.h
./tests/headers/union_with_big_member.h
./tests/headers/anon_union.hpp
./tests/headers/union_fields.hpp
./tests/headers/union_with_anon_struct_bitfield.h
./tests/headers/struct_with_anon_union.h
./tests/headers/union-in-ns.hpp
./tests/headers/union_with_anon_unnamed_union.h
./tests/headers/union_with_anon_struct.h
./tests/headers/union_with_nesting.h
./tests/headers/union_template.hpp
./tests/headers/anon_struct_in_union.h
./tests/headers/union_with_anon_unnamed_struct.h
~~~

~~~
$ ./tests/test-one.sh keywords
...
~~~

0 files changed, 0 insertions, 0 deletions