ci: Add JOBS variable to replace all the '-j4' instances. #5354

Job	Run time
dpdk gcc	6s
linux deb no dpdk	4m 36s
linux rpm fedora	4m 34s
osx clang --disable-ssl	3m 11s
linux gcc --disable-ssl	2m 3s
linux clang --disable-ssl	2m 16s
linux gcc c99	2m 3s
linux clang c99	2m 4s
linux gcc test	6m 22s
linux clang test asan	11m 17s
linux clang test ubsan	7m 32s
linux gcc test --enable-shared	8m 46s
linux clang test --enable-shared	8m 32s
linux gcc check check-dpdk dpdk	13m 51s
linux clang check check-dpdk dpdk	13m 29s
linux gcc test -ljemalloc	6m 44s
linux clang test -ljemalloc	6m 53s
linux gcc --enable-afxdp	2m 35s
linux clang --enable-afxdp	2m 12s
linux gcc dpdk --enable-shared	3m 4s
linux clang dpdk --enable-shared	3m 5s
linux gcc dpdk-shared	2m 17s
linux clang dpdk-shared	2m 22s
linux gcc dpdk-shared --enable-shared	3m 37s
linux clang dpdk-shared --enable-shared	2m 49s
linux gcc m32 --disable-ssl	2m 1s
	2h 8m 21s

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