controller, northd: Wait for cleanup before replying to exit #2359

Job	Run time
osx clang --disable-ssl	4m 4s
linux gcc --disable-ssl	3m 40s
linux clang --disable-ssl	4m 10s
linux gcc test -500	19m 19s
linux gcc test 501-1000	13m 52s
linux gcc test 1001-	7m 51s
linux clang test sanitizers -300	18m 21s
linux clang test sanitizers 301-600	23m 49s
linux clang test sanitizers 601-900	13m 28s
linux clang test sanitizers 901-1200	8m 32s
linux clang test sanitizers 1201-	9m 19s
linux gcc test -ljemalloc -500	19m 1s
linux gcc test -ljemalloc 501-1000	12m 51s
linux gcc test -ljemalloc 1001-	7m 11s
linux clang test -ljemalloc -500	22m 33s
linux clang test -ljemalloc 501-1000	14m 19s
linux clang test -ljemalloc 1001-	8m 40s
linux gcc system-test -100	12m 3s
linux gcc system-test 101-200	18m 43s
linux gcc system-test 201-	19m 11s
linux clang system-test sanitizers -100	14m 23s
linux clang system-test sanitizers 101-200	20m 26s
linux clang system-test sanitizers 201-	21m 27s
linux x86 gcc --disable-ssl	3m 57s
	5h 21m 10s

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