tests: Fix flaky "ovn-controller: Multiple OVS interfaces ...". #2567

Job	Run time
Prepare container	3m 25s
linux rpm fedora	7m 14s
osx clang --disable-ssl	2m 18s
linux gcc --disable-ssl	2m 45s
linux clang --disable-ssl	2m 40s
linux gcc test -300	10m 1s
linux gcc test 301-600	6m 58s
linux gcc test 601- unstable	7m 17s
linux clang test sanitizers -300	13m 37s
linux clang test sanitizers 301-600	9m 37s
linux clang test sanitizers 601- unstable	12m 31s
linux gcc test -ljemalloc -300	10m 27s
linux gcc test -ljemalloc 301-600	6m 58s
linux gcc test -ljemalloc 601- unstable	7m 21s
linux gcc system-test-dpdk dpdk -100	17m 1s
linux gcc system-test-dpdk dpdk 101- unstable	15m 45s
linux gcc system-test-userspace -100	15m 53s
linux gcc system-test-userspace 101- unstable	14m 46s
linux gcc system-test -100	18m 23s
linux gcc system-test 101- unstable	19m 22s
linux clang system-test sanitizers -100	20m 19s
linux clang system-test sanitizers 101- unstable	21m 4s
linux x86 gcc --disable-ssl	2m 44s
	4h 8m 26s

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