contrib: add qemu guest agent as an option for x86 #440

Job	Run time
generate_target_matrix	4s
build_firmware (ath79-generic)	1h 22m 55s
build_firmware (ath79-mikrotik)	1h 12m 29s
build_firmware (ath79-nand)	1h 14m 28s
build_firmware (bcm27xx-bcm2708)	1h 6m 32s
build_firmware (bcm27xx-bcm2709)	1h 16m 51s
build_firmware (bcm27xx-bcm2710)	1h 18m 55s
build_firmware (bcm27xx-bcm2711)	1h 19m 58s
build_firmware (ipq40xx-generic)	1h 15m 45s
build_firmware (ipq40xx-mikrotik)	1h 16m 39s
build_firmware (ipq806x-generic)	1h 14m 51s
build_firmware (lantiq-xrx200)	1h 18m 27s
build_firmware (lantiq-xway)	1h 14m 9s
build_firmware (mediatek-mt7622)	1h 17m 13s
build_firmware (mpc85xx-p1010)	1h 14m 30s
build_firmware (mpc85xx-p1020)	1h 12m 38s
build_firmware (mvebu-cortexa9)	1h 16m 56s
build_firmware (ramips-mt7620)	1h 13m 49s
build_firmware (ramips-mt7621)	1h 20m 15s
build_firmware (ramips-mt76x8)	1h 14m 10s
build_firmware (realtek-rtl838x)	1h 1m 27s
build_firmware (rockchip-armv8)	1h 23m 23s
build_firmware (sunxi-cortexa7)	1h 7m 59s
build_firmware (x86-64)	1h 28m 23s
build_firmware (x86-generic)	1h 23m 14s
build_firmware (x86-geode)	1h 22m 41s
build_firmware (x86-legacy)	1h 21m 45s
create_release	0s
	1d 9h 10m 26s

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