lib/terminal.py: Add urxvt terminal

lib/terminal.py: Add urxvt terminal

This fixes failure [1] of menuconfig task in rxvt-unicode terminal in case if
xterm/Konsole/Gnome is not installed. Tested with rxvt-unicode-256color

[1]
WARNING: Terminal screen is supported but did not start
ERROR: No valid terminal found, unable to open devshell.
Tried the following commands:
	tmux split-window -c "{cwd}" "do_terminal"
	tmux new-window -c "{cwd}" -n "zephyr-helloworld Configuration" "do_terminal"
	xfce4-terminal -T "zephyr-helloworld Configuration" -e "do_terminal"
	terminology -T="zephyr-helloworld Configuration" -e do_terminal
	mate-terminal --disable-factory -t "zephyr-helloworld Configuration" -x do_terminal
	konsole --separate --workdir . -p tabtitle="zephyr-helloworld Configuration" -e do_terminal
	gnome-terminal -t "zephyr-helloworld Configuration" -- do_terminal
	xterm -T "zephyr-helloworld Configuration" -e do_terminal
	rxvt -T "zephyr-helloworld Configuration" -e do_terminal
	tmux new -c "{cwd}" -d -s devshell -n devshell "do_terminal"
	screen -D -m -t "zephyr-helloworld Configuration" -S devshell do_terminal
DEBUG: Python function do_menuconfig finished

Signed-off-by: Pavel Zhukov <pazhukov@suse.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>