sesman: address the issue of socket file leftovers
sesman: address the issue of socket file leftovers

There are two points.

Make sure cleanup files happen after chansrv and Xserver exit. If these
child processes lock socket files, the deletion might fail.

Usually, cleanup of xorgxrdp related socket files is handled by
xorgxrdp. Just in case it failed, perform cleanup also in sesman.

Fixes #1740. Thanks to @matt335672.

Sponsored by:   Cybertrust Japan
Sponsored by:   HAW International

PKRoma/xrdp,neutrinolabs/xrdp,neutrinolabs/xrdp,metalefty/xrdp,metalefty/xrdp,PKRoma/xrdp,neutrinolabs/xrdp,PKRoma/xrdp,metalefty/xrdp