qa/workunits/cephtool/test.sh: refactor and make it modular (yey! \o/)

Instead of having this monolithic bunch of commands in a sequence, refactor the test
so that we have function, allowing us to keep the same sequence of operations AND
to call for individual tests (as many times, in whatever order as we want).

Although we tried to split the commands as best as we could without spending too
much time on it, there's still a lot of them that look like they could have been better
split.  There's also the matter of figuring out whether some of the commands depend
on previous commands within the same function, or if they could be simply moved to
a function of their own.

Loic reviewed most of this branch on branch 'wip-8624-with-amazing-foo', prior to
rebase, conflict fixing and addition of the last commit on the patch series (which has
the test checking if the monitors have tcmalloc enabled prior to running the heap
profiler tests, thus dropping the (ab)use of 'set +e').

Currently still waiting for the branch to go through the gitbuilders make checks.

Upon merge, 'wip-8624-with-amazing-foo' should also be removed.  Keeping it
just for Loic's reviews in case anyone wants to take a look.