github: Fix image not being updated on re-run. #203

Job	Run time
linux rpm fedora	6m 57s
Prepare container	3m 49s
osx clang --disable-ssl	1m 52s
linux gcc --disable-ssl	7s
linux clang --disable-ssl	7s
linux gcc test -300	8s
linux gcc test 301-600	5s
linux gcc test 601- unstable	5s
linux clang test sanitizers -300	5s
linux clang test sanitizers 301-600	6s
linux clang test sanitizers 601- unstable	5s
linux gcc test -ljemalloc -300	6s
linux gcc test -ljemalloc 301-600	6s
linux gcc test -ljemalloc 601- unstable	9s
linux gcc system-test-dpdk dpdk -100	4s
linux gcc system-test-dpdk dpdk 101- unstable	5s
linux gcc system-test-userspace -100	6s
linux gcc system-test-userspace 101- unstable	5s
linux gcc system-test -100	8s
linux gcc system-test 101- unstable	8s
linux clang system-test sanitizers -100	6s
linux clang system-test sanitizers 101- unstable	6s
linux x86 gcc --disable-ssl	8s
	14m 43s

Provide feedback