'attach' option for init.sh;

To easily attach the console of production system
just by entering `./init.sh attach' command.

Signed-off-by: Tomas Morstein <tmr&idea.cz>
rebar plugin: erl_command() instead of "erl" const;

Signed-off-by: Tomas Morstein <tmr&idea.cz>
Merge pull request #286 from ztmr/master

Support for `init.sh attach'