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

Boolean null is casted to boolean.

Change-Id: I1ef9490664a663db1aaf2fa14da239df01d78bab
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>
Signed-off-by: Gustavo Pedrosa <gustavo.pedrosa@eldorado.org.br>