Ceph make -j8 check in less than 3mn

The Ceph sources contain tests that can be run with make check. As of v0.85 then can only be run sequentially because some tests bind the same ports and use the same files. It takes around 18 minutes on a spinner and 12 minutes on a SSD because of some I/O intensive ones. It becomes problematic because it’s a long time to wait when adding code and trying to validate it works and also because it keeps increasing as more tests are added. It’s also a recurring frustration because they conflict with vstart.sh cluster running for manual testing.
The tests have been reworked to ensure that none of them use the the same port or the same files. It reduces the time to 12mn on a spinner and around 2mn on a SSD with make -j8 check.

[loic@rex001 src]$ time make -j8 check
make[4]: Entering directory `/home/loic/ceph/src'
./check_version ./.git_version
make[1]: Leaving directory `/home/loic/ceph/src'

real    2m21.907s
user    5m45.958s
sys     1m50.431s

A number of tests such as qa/workunits/cephtool/test.sh take a long time but do not require much CPU or disk I/O. When on a 4 core machine setting -j8 gives a chance for these tests to run while more CPU intensive tests are using most of the CPU power.
Using larger values (for instance -j16) does not help much because a few tests take around 3mn to run anyway.