Changed linkage around libjvm to use dlopen.

The dependency on libjvm is a "hard", requiring an link and rpath.
This causes issues when shifting between jvms. The standard practice
is to use dlopen against the $JAVA_JVM_LIBRARY location.

MESOS-1126
    + Enable dlopen for libjvm.so
    + Cleanup redundant jni inclusions

This should make MESOS-855 a non-issue.

Review: https://reviews.apache.org/r/19487