vif-plug: Avoid Transaction failures in ovsdb. #1418

Job	Run time
linux rpm fedora	7m 12s
osx clang --disable-ssl	1m 56s
Prepare container	1m 10s
linux gcc --disable-ssl	2m 52s
linux clang --disable-ssl	2m 36s
linux gcc test -300	9m 11s
linux gcc test 301-600	6m 9s
linux gcc test 601- unstable	6m 15s
linux clang test sanitizers -300	12m 39s
linux clang test sanitizers 301-600	8m 54s
linux clang test sanitizers 601- unstable	10m 27s
linux gcc test -ljemalloc -300	9m 50s
linux gcc test -ljemalloc 301-600	6m 24s
linux gcc test -ljemalloc 601- unstable	6m 31s
linux gcc system-test-dpdk dpdk -100	16m 57s
linux gcc system-test-dpdk dpdk 101- unstable	14m 7s
linux gcc system-test-userspace -100	16m 8s
linux gcc system-test-userspace 101- unstable	13m 4s
linux gcc system-test -100	18m 20s
linux gcc system-test 101- unstable	16m 44s
linux clang system-test sanitizers -100	20m 7s
linux clang system-test sanitizers 101- unstable	18m 40s
linux x86 gcc --disable-ssl	2m 57s
	3h 49m 10s

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