AdbHostTest: don't run against emulators.

Bug: http://b/158317051
Test: treehugger
Change-Id: I4186d1714c909f20ea9a5a4d6c593bba84208059
diff --git a/hostsidetests/adb/src/android/adb/cts/AdbHostTest.java b/hostsidetests/adb/src/android/adb/cts/AdbHostTest.java
index 11a1ae0..bea7506 100644
--- a/hostsidetests/adb/src/android/adb/cts/AdbHostTest.java
+++ b/hostsidetests/adb/src/android/adb/cts/AdbHostTest.java
@@ -59,8 +59,13 @@
         File check_ms_os_desc = copyResourceToTempFile("/check_ms_os_desc");
         check_ms_os_desc.setExecutable(true);
 
+        String serial = getDevice().getSerialNumber();
+        if (serial.startsWith("emulator-")) {
+            return;
+        }
+
         ProcessBuilder pb = new ProcessBuilder(check_ms_os_desc.getAbsolutePath());
-        pb.environment().put("ANDROID_SERIAL", getDevice().getSerialNumber());
+        pb.environment().put("ANDROID_SERIAL", serial);
         pb.redirectOutput(ProcessBuilder.Redirect.PIPE);
         pb.redirectErrorStream(true);
         Process p = pb.start();