title: Cannot run powermockrule with SpringJUnit4ClassRunner in spring boot project
body: <p>I have a spring boot project that needs to test with spring test runner(so that I can get the real application context) and mock the static method.</p>
  
  <pre><code>@RunWith(SpringJUnit4ClassRunner.class)
  @SpringApplicationConfiguration(classes= MyApplication.class)
  @PrepareForTest(StaticClass.class)
  public class StaticClassTest {
  
      @Rule
      public PowerMockRule rule = new PowerMockRule();
  
      @Autowired
      HelloCmd hello;
  
      @Test
      public void testGetOne() {
          mockStatic(StaticClass.class);
          when(StaticClass.getNumber()).thenReturn(2);
          System.out.println(hello.getNumber());
      }
  }
  </code></pre>
  
  <p>And I got following error message when run the test:</p>
  
  <pre><code>com.thoughtworks.xstream.converters.ConversionException: hello.hystrix.commands.HelloCmd$$EnhancerBySpringCGLIB$$a27be1be : hello.hystrix.commands.HelloCmd$$EnhancerBySpringCGLIB$$a27be1be
  ---- Debugging information ----
  message             : hello.hystrix.commands.HelloCmd$$EnhancerBySpringCGLIB$$a27be1be
  cause-exception     : com.thoughtworks.xstream.mapper.CannotResolveClassException
  cause-message       : hello.hystrix.commands.HelloCmd$$EnhancerBySpringCGLIB$$a27be1be
  class               : hello.hystrix.commands.StaticClassTest
  required-type       : hello.hystrix.commands.StaticClassTest
  converter-type      : com.thoughtworks.xstream.converters.reflection.ReflectionConverter
  path                : /org.powermock.modules.junit4.rule.PowerMockStatement$1/outer-class/fNext/next/next/target/hello
  line number         : 15
  class[1]            : org.junit.internal.runners.statements.InvokeMethod
  class[2]            : org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks
  class[3]            : org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks
  class[4]            : org.powermock.modules.junit4.rule.PowerMockStatement
  class[5]            : org.powermock.modules.junit4.rule.PowerMockStatement$1
  version             : null
  </code></pre>
  
  <p>How to fix this? Thanks!</p>