JNI: cleaner code around setProperty
JNI: cleaner code around setProperty

Better variable names, less intermediates, using auto when possible,
prevents a potential leak.

Change-Id: I4efb8f506dd2171591d526afcd04e8bf53b50ef0
Reviewed-on: http://gerrit.aldebaran.lan/77668
Reviewed-by: jmonnon <8898eaf233516e520f996a244ca8a12d20f948b1@aldebaran.com>
Tested-by: vpaleologue <cb19838a79eb484e12a6960acfbf7c16dfdb80d9@aldebaran-robotics.com>

aldebaran/libqi-java,aldebaran/libqi-java,aldebaran/libqi-java