ci: Add JOBS variable to replace all the '-j4' instances. #5358

Job	Run time
linux rpm fedora	5m 16s
osx clang --disable-ssl	3m 5s
dpdk gcc	6s
linux deb no dpdk	4m 53s
linux gcc --disable-ssl	2m 23s
linux clang --disable-ssl	2m 20s
linux gcc c99	2m 33s
linux clang c99	2m 15s
linux gcc test	6m 35s
linux clang test asan	11m 23s
linux clang test ubsan	7m 8s
linux gcc test --enable-shared	9m 2s
linux clang test --enable-shared	8m 50s
linux gcc check check-dpdk dpdk	13m 27s
linux clang check check-dpdk dpdk	13m 51s
linux gcc test -ljemalloc	6m 49s
linux clang test -ljemalloc	7m 11s
linux gcc --enable-afxdp	2m 7s
linux clang --enable-afxdp	2m 9s
linux gcc dpdk --enable-shared	3m 21s
linux clang dpdk --enable-shared	3m 19s
linux gcc dpdk-shared	2m 23s
linux clang dpdk-shared	2m 16s
linux gcc dpdk-shared --enable-shared	3m 13s
linux clang dpdk-shared --enable-shared	2m 40s
linux gcc m32 --disable-ssl	2m 10s
	2h 10m 45s

Provide feedback