Code review comment for lp:~asc/fluidity/testharnesscwd2

The motivation for the change is to:

 1. Use the script from a $PATH location,
 2. on a given test folder (which might be standalone),
 3. from an arbitrary location (already possible before the above, but more complicated in combination with 1 and 2).

Point 1 was because I have several modifications to the testharness.py and just wanted to use one instance of the script for multiple branches (e.g. place it in ~/bin) and point 2 because I have some tests in a standalone folder that I have been testing using multiple branches.

Of course there is an issue with 2, in that tests can have dependencies within the Fluidity source (in the mesh generation, for example). This could work if it was possible to provide the root Fluidity folder (for the binary and other test dependencies) together with the location of the test folder (the default being ../ and ../{examples,tests,longtests} respectively).

As it stands the changes need further thought, so I'll pull the merge request for now. It is possible to use with the limitations that the script itself, binary and associated tools must all be located in the Fluidity source tree, together with the folder of tests.