northd: Don't monitor most of northbound external IDs. #230

Job	Run time
linux rpm fedora	6m 31s
osx clang --disable-ssl	2m 25s
Prepare container	3m 48s
linux gcc --disable-ssl	2m 39s
linux clang --disable-ssl	2m 49s
linux gcc test -300	9m 17s
linux gcc test 301-600	6m 19s
linux gcc test 601- unstable	6m 28s
linux clang test sanitizers -300	12m 46s
linux clang test sanitizers 301-600	9m 20s
linux clang test sanitizers 601- unstable	10m 43s
linux gcc test -ljemalloc -300	10m 2s
linux gcc test -ljemalloc 301-600	6m 30s
linux gcc test -ljemalloc 601- unstable	6m 39s
linux gcc system-test-dpdk dpdk -100	17m 17s
linux gcc system-test-dpdk dpdk 101- unstable	14m 13s
linux gcc system-test-userspace -100	15m 58s
linux gcc system-test-userspace 101- unstable	13m 6s
linux gcc system-test -100	20m 16s
linux gcc system-test 101- unstable	16m 42s
linux clang system-test sanitizers -100	20m 12s
linux clang system-test sanitizers 101- unstable	20m 41s
linux x86 gcc --disable-ssl	2m 35s
	3h 57m 16s

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