Give a clear error message if we can't start the server.

Bug: http://b/35218713
Test: adb kill-server ; export HOME=/ ; adb devices
Change-Id: I53cc30213be0eab84e42b09c7b501362d6e44b05
diff --git a/adb_utils.h b/adb_utils.h
index 11c0ec9..f764a0e 100644
--- a/adb_utils.h
+++ b/adb_utils.h
@@ -89,4 +89,6 @@
     }
 };
 
+std::string GetLogFilePath();
+
 #endif