perf-northd.at: Add ovn-northd recompute statistics. #2486

Job	Run time
dpdk gcc	19s
linux rpm fedora	6m 59s
osx clang --disable-ssl	3m 40s
linux gcc --disable-ssl	1m 53s
linux clang --disable-ssl	1m 55s
linux gcc test -300	8m 24s
linux gcc test 301-600	5m 29s
linux gcc test 601- unstable	5m 1s
linux clang test sanitizers -300	11m 21s
linux clang test sanitizers 301-600	8m 2s
linux clang test sanitizers 601- unstable	8m 41s
linux gcc test -ljemalloc -300	8m 54s
linux gcc test -ljemalloc 301-600	5m 32s
linux gcc test -ljemalloc 601- unstable	5m 10s
linux gcc system-test-dpdk dpdk -100	12m 45s
linux gcc system-test-dpdk dpdk 101- unstable	12m 1s
linux gcc system-test-userspace -100	11m 26s
linux gcc system-test-userspace 101- unstable	10m 57s
linux gcc system-test -100	14m 9s
linux gcc system-test 101- unstable	12m 29s
linux clang system-test sanitizers -100	15m 49s
linux clang system-test sanitizers 101- unstable	14m 10s
linux x86 gcc --disable-ssl	1m 52s
	3h 6m 58s

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