java: mraa jni library now dynamically links to libmraa

libmraajava.so was statically linking to mraa object files causing
duplicate mraa platform instances if a UPM Java module was also loaded.

JNI functionality has been moved into src/java/mraajni.c. JVM object is
now set when JVM is loaded; see updates to src/java/mraajava.i.
This was necessary as the JVM object cannot be directly referenced from
mraa as it will not be available when building C/C++ examples.

Signed-off-by: Henry Bruce <henry.bruce@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

src/java/mraajava.i

@@ -65,11 +65,11 @@ class Spi;
 %include ../mraa.i
 
 %wrapper %{
-    JavaVM *globVM;
+    #include "java/mraajni.h"
 
     jint JNI_OnLoad(JavaVM *vm, void *reserved) {
         /* initialize mraa */
-        globVM = vm;
+        mraa_java_set_jvm(vm);
         mraa_init();
         return JNI_VERSION_1_6;
     }