don't waste people's lifetime in init_tmp_cleaner

close stdin, stdout, stderr in init_tmp_cleaner

this makes nslave recognize a bit faster that mw-render has finished
since it won't wait for mw-render's child process - which just does an
rmtree - to finish.
fix possible problems on solaris containers in init_tmp_cleaner

we now wait for the parent process id to change instead of it becoming
1. it looks like the parent process id is not always 1 on solaris
containers for orphaned processes.