This commit moves the handling of distribution config and starting out
of rebar_prv_shell and into rebar_dist_utils. The module is able to
handle standard config options and boot a distributed node mode. This
could be used in plugins (once it is exposed) and other providers like
CT.
Configuration is also expanded so that options like:
{dist, [{sname, atom()}, {name, atom()}, {setcookie, term()}]}
can be used and will be handled as a default. The config handler
supports similar terms from the command line being parsed in if the
calling provider supports them.
A test suite is added for configuration handling.
Fred Hebert