core: [Fix] NPE in update vm/template (via rest)

Boolean null is casted to boolean.

Change-Id: If715acc7a0cbcf719f636cad6b9327f65cf3813c
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1059780
Signed-off-by: Gustavo Pedrosa <gustavo.pedrosa@eldorado.org.br>