Fixed RunCommandDropRoot when running as Shell.

BUG: 26379932
BUG: 31807540

Test: mmm -j32 frameworks/native/cmds/dumpstate/ && adb push ${ANDROID_PRODUCT_OUT}/data/nativetest/dumpstate_test* /data/nativetest&& adb unroot && adb shell /data/nativetest/dumpstate_test/dumpstate_test

Change-Id: Id582f5fbd4d6282a2eacce602ae1a6d1f62d5c61
diff --git a/cmds/dumpstate/tests/dumpstate_test.cpp b/cmds/dumpstate/tests/dumpstate_test.cpp
index d2d5b40..60ac6d1 100644
--- a/cmds/dumpstate/tests/dumpstate_test.cpp
+++ b/cmds/dumpstate/tests/dumpstate_test.cpp
@@ -306,7 +306,7 @@
     EXPECT_EQ(0, RunCommand("", {simpleCommand, "--uid"},
                             CommandOptions::WithTimeout(1).DropRoot().Build()));
     EXPECT_THAT(out, StrEq("2000\nstdout\n"));
-    EXPECT_THAT(err, StrEq("stderr\n"));
+    EXPECT_THAT(err, StrEq("drop_root_user(): already running as Shell\nstderr\n"));
 }
 
 TEST_F(DumpstateTest, RunCommandAsRootUserBuild) {