Updates to allow executing fvp from the container

This change configures locale information that xterm needs to allow to
launch gui terminals inside the running container.
An environment variable 'DISPLAY' is also introduced in the docker run
command, to configure a display for the container.

Signed-off-by: Nuno Lopes <nuno.lopes@arm.com>
Change-Id: I4e23fdcc2821f454abf1257cd719825651e469fc