collectd: fix a floating dependence on openjdk

1. fix a floating dependence on openjdk
2. fix the host contamination, since the default value of java home
is /usr/lib/jvm:
   warning: library search path "/usr/lib/jvm/jre-1.7.0/lib/amd64/server" is unsafe for cross-compilation

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>