checkpatch.py: Port checkpatch related changes from the OVS repo. #2598

Job	Run time
dpdk gcc	4s
osx clang --disable-ssl	4m 11s
linux rpm fedora	7m 7s
Prepare container	2m 11s
linux gcc --disable-ssl	2m 19s
linux clang --disable-ssl	2m 19s
linux gcc test -500	14m 10s
linux gcc test 501-1000	10m 20s
linux gcc test 1001-	5m 23s
linux clang test sanitizers -300	11m 20s
linux clang test sanitizers 301-600	14m 9s
linux clang test sanitizers 601-900	9m 19s
linux clang test sanitizers 901-1200	7m 52s
linux clang test sanitizers 1201-	6m 38s
linux gcc test -ljemalloc -500	15m 43s
linux gcc test -ljemalloc 501-1000	10m 46s
linux gcc test -ljemalloc 1001-	5m 38s
linux gcc system-test-dpdk dpdk -100	10m 55s
linux gcc system-test-dpdk dpdk 101-200	15m 35s
linux gcc system-test-dpdk dpdk 201-	22m 33s
linux gcc system-test-userspace -100	10m 2s
linux gcc system-test-userspace 101-200	13m 54s
linux gcc system-test-userspace 201-	21m 20s
linux gcc system-test -100	13m 8s
linux gcc system-test 101-200	16m 9s
linux gcc system-test 201-	23m 33s
linux clang system-test sanitizers -100	14m 49s
linux clang system-test sanitizers 101-200	17m 56s
linux clang system-test sanitizers 201-	25m 47s
linux x86 gcc --disable-ssl	2m 29s
	5h 37m 39s

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