test: add missing thread test prerequisite.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
test: set thread id only if python-yaml is present.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
Merge pull request #14 from eroullit/thread-test-fix

Thread test fix with python-yaml is not present