Set umask before creating conffile
Write username/password to torsocks config

This fixes a bug, because torsocks since version 1.0-delta uses
TORSOCKS_* instead of TSOCKS_* for the environment variables.
See https://gitweb.torproject.org/torsocks.git/commit/23818494dcaad8339445f4f6ac948ede5a72b8e4

Using the configuration file should also be safer in general and
backwards-compatible.