psh: reimplement 'kill' command #924

Job	Run time
call-ci / build (armv7a7-imx6ull-evk)	1m 16s
call-ci / build (armv7a9-zynq7000-qemu)	1m 19s
call-ci / build (armv7a9-zynq7000-zedboard)	1m 15s
call-ci / build (armv7a9-zynq7000-zturn)	1m 1s
call-ci / build (armv7m4-stm32l4x6-nucleo)	1m 7s
call-ci / build (armv7m7-imxrt105x-evk)	1m 23s
call-ci / build (armv7m7-imxrt106x-evk)	1m 11s
call-ci / build (armv7m7-imxrt117x-evk)	1m 23s
call-ci / build (host-generic-pc)	48s
call-ci / build (ia32-generic-pc)	1m 4s
call-ci / build (ia32-generic-qemu)	1m 15s
call-ci / build (riscv64-generic-qemu)	59s
call-ci / build (riscv64-generic-spike)	58s
call-ci / build (sparcv8leon3-gr716-mini)	54s
call-ci / test EMU (armv7a9-zynq7000-qemu)	17s
call-ci / test EMU (host-generic-pc)	18s
call-ci / test HW (armv7a7-imx6ull-evk)	31s
call-ci / test EMU (ia32-generic-qemu)	13s
call-ci / test HW (armv7m7-imxrt106x-evk)	23s
call-ci / test EMU (riscv64-generic-qemu)	15s
call-ci / test HW (armv7m7-imxrt117x-evk)	20s
call-ci / test HW (armv7a9-zynq7000-zedboard)	19s
call-ci / test HW (armv7m4-stm32l4x6-nucleo)	21s
call-ci / tests-summary	7s
call-ci / send-notification	0s
	18m 57s

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