LCGDM-2955 fix draining in with stopped legacy DPM
It is not possible to drain disknode with legacy python2-dpm (python36-dpm) packages installed, because dmlite-shell try to contact legacy DPM daemons and if they are no longer running an attempt to talk with them hangs.
This patch use similar approach used by infoservice to detect running legacy DPM (lists all ports in LISTENING state and checks if DPM daemon listens on port 5015/tcp).