Build odl plugin with openjdk-8

Build odl plugin with openjdk-8

Daniel Smith discover large resource consumption when SFC features are
enabled and openjdk-7 is used. Following his advice we want to add
option to use openjdk-8. Becuase this version is not offically available
in ubuntu 14.04, it needs to be included inside plugin. This can be
achieved by setting USE_JAVA8=true environment variable during plugin compilation

Change-Id: Id029a00cea24d264b3c121e6adc50581b9ae1c9a
Signed-off-by: Michal Skalski <mskalski@mirantis.com>