contrib: add qemu guest agent as an option for x86 #431

Job	Run time
generate_target_matrix	2s
build_firmware (ath79-generic)	1h 24m 10s
build_firmware (ath79-mikrotik)	1h 16m 27s
build_firmware (ath79-nand)	1h 15m 35s
build_firmware (bcm27xx-bcm2708)	1h 8m 29s
build_firmware (bcm27xx-bcm2709)	1h 16m 46s
build_firmware (bcm27xx-bcm2710)	1h 20m 29s
build_firmware (bcm27xx-bcm2711)	1h 19m 43s
build_firmware (ipq40xx-generic)	1h 16m 41s
build_firmware (ipq40xx-mikrotik)	1h 13m 35s
build_firmware (ipq806x-generic)	1h 18m 2s
build_firmware (lantiq-xrx200)	1h 19m 25s
build_firmware (lantiq-xway)	1h 14m 15s
build_firmware (mediatek-mt7622)	1h 20m 51s
build_firmware (mpc85xx-p1010)	1h 14m 6s
build_firmware (mpc85xx-p1020)	1h 14m 36s
build_firmware (mvebu-cortexa9)	1h 14m 31s
build_firmware (ramips-mt7620)	1h 16m 22s
build_firmware (ramips-mt7621)	1h 22m 0s
build_firmware (ramips-mt76x8)	1h 16m 30s
build_firmware (realtek-rtl838x)	1h 1m 49s
build_firmware (rockchip-armv8)	1h 20m 23s
build_firmware (sunxi-cortexa7)	1h 10m 25s
build_firmware (x86-64)	1h 29m 33s
build_firmware (x86-generic)	1h 24m 48s
build_firmware (x86-geode)	1h 19m 27s
build_firmware (x86-legacy)	1h 21m 26s
create_release	0s
	1d 9h 30m 26s

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