Compile error of UnixOperationSystemMXBean with open JDK

zookeeper invokes getOpenFileDescriptorCount() function in com.sun.management.UnixOperatingSystemMXBean, which only exists in SUN JDK, and open JDK did not implement this function.

[javac] /root/zookeeper-3.3.4/src/java/test/org/apache/zookeeper/test/ClientBase.java:57: package com.sun.management does not exist
[javac] import com.sun.management.UnixOperatingSystemMXBean;
[javac] ^
[javac] /root/zookeeper-3.3.4/src/java/test/org/apache/zookeeper/test/QuorumBase.java:39: package com.sun.management does not exist
[javac] import com.sun.management.UnixOperatingSystemMXBean;
[javac] ^
[javac] /root/zookeeper-3.3.4/src/java/test/org/apache/zookeeper/test/ClientTest.java:48: package com.sun.management does not exist
[javac] import com.sun.management.UnixOperatingSystemMXBean;
[javac] ^
[javac] /root/zookeeper-3.3.4/src/java/test/org/apache/zookeeper/test/QuorumUtil.java:39: package com.sun.management does not exist
[javac] import com.sun.management.UnixOperatingSystemMXBean;