proxy dockerfile #3647

Job	Run time
multiple-arch-armv7	22m 7s
cygwin64-cache	1m 45s
utest-regression-blackbox-test	9m 32s
multiple-arch-aarch64	22m 55s
cygwin64	15m 19s
fast	1s
build-ubuntu18	3m 3s
build-ubuntu20	3m 29s
build-cross-aarch64	5m 4s
build-centos7	4m 52s
build-cross-arm	5m 8s
build-ubuntu16	3m 4s
coverage	3m 32s
multiple-arch-amd64	2m 26s
test-done	2s
	1h 42m 19s

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