Add JDK (Java Develop Kit) to Dockerfile.mobile

As title.

test=develop

paddle/fluid/lite/tools/Dockerfile.mobile

@@ -39,7 +39,8 @@ RUN apt-get install -y --no-install-recommends \
         lib32stdc++6 \
         redir \
         iptables \
-        openjdk-8-jre
+        openjdk-8-jre \
+        default-jdk
 
 # for cmake 3.10
 RUN curl -O https://mms-res.cdn.bcebos.com/cmake-3.10.3-Linux-x86_64.tar.gz && \