bug in parallel tests

[yiminc-zz]

When enable parallel testing, we would expect the TearDownSuite() to be called after all the tests completed. However, after this commit, 3104bf5
the parallel testing is broken as the TearDownSuite() is called before tests are done.
Here is a simple repro code to repro:

type MyTestSuite struct {
	suite.Suite
}
func TestMySuite(t *testing.T) {
	suite.Run(t, new(MyTestSuite))
}
func (s *MyTestSuite) SetupSuite() {
	fmt.Println("SetupSuite")
}
func (s *MyTestSuite) TearDownSuite() {
	fmt.Println("TearDownSuite")
}
func (s *MyTestSuite) SetupTest() {
	s.T().Parallel()
	fmt.Println("SetupTest")
}
func (s *MyTestSuite) TearDownTest() {
	fmt.Println("TearDownTest")
}
func (s *MyTestSuite) Test_A() {
	time.Sleep(time.Second)
}
func (s *MyTestSuite) Test_B() {
	time.Sleep(time.Second * 2)
}

The output of above tests is:

SetupSuite
TearDownSuite
SetupTest
SetupTest
TearDownTest
TearDownTest

[thaJeztah]

relates to #389, #346

/cc @bayesianmind @ernesto-jimenez PTAL

[piepmatz]

The same problem applies to parallel subtests: TearDownTest() is run before the test is completed.