Make the TSC use /var/run/ for creating the unix socket

The current implementation of the TSC opens a unix socket in /tmp/tsc.sock.

The current convention in OSes following the XDG specs is to use the path in $XDG_RUNTIME_DIR[1], which, in systemd-based OSes, is set to /var/run/user/$UID/.

In the centos:7 docker environment $XDG_RUNTIME_DIR is not defined.

The proposed solution is to access the $XDG_RUNTIME_DIR environment variable and keep /tmp/tsc.sock as a fallback.