Explictly use env to setup needed environment variables for dnsmasq when
starting to avoid problems with subprocess mis-interpreting the first
command line argument as the executable name.
Also update DnsmasqFilter to accept any command that starts with env
followed by a set of args that include an equals sign, as long as the
next arg is the dnsmasq command.
fixes bug #1073253
Change-Id: I8ac08ba2d2309934a67ed2cb28049ed5d3277d63