Fix tests for matching instructors
Fix tests for matching instructors

3 tests were removed since they tested matching specific number of
instructors returned ('wanted' instructors).

1 test was added: it tests matching by country.

self.client invocations were fixed (POST → GET).

swcarpentry/amy,wking/swc-amy,pbanaszkiewicz/amy,pbanaszkiewicz/amy,vahtras/amy,vahtras/amy,pbanaszkiewicz/amy,swcarpentry/amy,wking/swc-amy,vahtras/amy,wking/swc-amy,wking/swc-amy,swcarpentry/amy