tuxrun: add support for --qemu-binary to use host binary

We achieve this by utilising two features of the docker container. First we bind all the paths for each library the binary is linked to under "/opt/host". We then pass an appropriately cooked environment variable LD_LIBRARY_PATH into the container to trigger the lookup of libraries from there first. This way the host built binary can run under inside the containers runtime environment.

Signed-off-by: Alex Bennée alex.bennee@linaro.org