lib: better test name filtering

Limited glob matching with leading or trailing '*'.

Tests (and globs of tests) can be excluded by prepending with a '-'.

Signed-off-by: Peter Feiner <pfeiner@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20170421005004.137260-6-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>