Fix for the issue #17225 flaky test DockerSuite.TestExecEnv test case.

This is done by calling waitRun() followed by the docker run, which ensures the container is loaded
before calling docker exec to obtain the env variable set previously.

Incorporated the change as suggeted by duglin.

Signed-off-by: Anil Belur <askb23@gmail.com>

integration-cli/docker_cli_exec_test.go

@@ -127,6 +127,7 @@ func (s *DockerSuite) TestExecEnv(c *check.C) {
 	testRequires(c, DaemonIsLinux)
 	dockerCmd(c, "run", "-e", "LALA=value1", "-e", "LALA=value2",
 		"-d", "--name", "testing", "busybox", "top")
+	c.Assert(waitRun("testing"), check.IsNil)
 
 	out, _ := dockerCmd(c, "exec", "testing", "env")
 	if strings.Contains(out, "LALA=value1") ||