Fix a bunch of shell-quoting issues

This fixes adding multiple argument to DOCKER_ARGS in dvm.conf, e.g.:

    export DOCKER_ARGS="--dns 192.0.2.88 --dns 192.0.2.44"
Fix DOCKER_ARGS having no effect.

EXTRA_ARGS was not being exported (and apparently busybox forks before
expanding args?)

The docker process now seems to actually receive the extra args.
Add parens to #shq method in Vagrantfile.

References #41
Merge branch 'dlitz-fix-docker-args' #41