Apply workaround for slow testtool device creation

Apply workaround for slow testtool device creation

According to the ODL Wiki [0], the testtool may take long
time to create the devices. As this tends to be the case
almost always (on sandbox it takes about 2 seconds per
device, on a DELL notebook running Manjaro Linux in
VirtualBox on top of Windows 7, it can take as much as 30
seconds per device), add the workaround into the
default Java options to avoid the problem.

[0] https://wiki.opendaylight.org/view/OpenDaylight_Controller:Netconf:Testtool#Slow_creation_of_devices_on_virtual_machines

Change-Id: I850e86284b403f45a0254c912b1ce6535dac476e
Signed-off-by: Jozef Behran <jbehran@cisco.com>