node_manager_fkie: fixed a problem with screen view

The node_manager uses the /usr/bin/x-terminal-emulator to show the
screen content of the nodes. To execute a command with arguments
'konsole', 'xterm' uses -e, 'terminator', 'gnome-terminal' or
'xfce4-terminal'use '-x'.
Merge branch 'master' into discovery_test
Merge branch 'discovery_test' of https://github.com/fkie/multimaster_fkie into discovery_test