PIPE_DIR handling
PIPE_DIR handling

As mentioned in the (closed) issue #127, the default pipe directory is not multi-user friendly. When running multiple relx-generated releases as different users, the first to be started will create the /tmp/erl_pipes directory, which the ones starting after that cannot create their pipe dirs in. The ticket mentions that this should be fixed by #154, but I cannot see how this is supposed to solve the issue. Right now, the only way I see is to use prefix the start command with env PIPE_DIR=/some/other/dir/, which is quite cumbersome.
This change will work exactly as before when PIPE_DIR is explicitly set. In case PIPE_DIR is not set, however, it will first attempt to create the parent dir /tmp/erl_pipes with mode 1777, which should enable releases being run as other users to create their pipe dirs.
erlware/relx,tsloughter/relx,lrascao/relx