Add support for parallel checks in HAVM

We cannot safely run make check -j2 nor make distcheck -j2 at the moment in the HAVM build tree. The tests run by these targets (tests/cmp.test and tests/trace.test) write and read the same files (located in `tests/testSubDir/), which prevent any safe concurrent execution.

I (Roland) have removed the « -j » options of the make check and make distcheck steps of HAVM's TeamCity builds (see https://teamcity.lrde.epita.fr/viewType.html?buildTypeId=Havm_X8664unknownLinuxGnu&tab=buildTypeSettings). Anyhow we shall add support for concurrent runs to HAVM's test engine.