Improvements to parallel self test

* Automatically extract oomph_root from Makefile if possible

* Don't try to record a list of test passes
  The idea was flawed: tests can have changed without needed to be rebuilt
  (e.g. if a .cc file changes).
Add paranoid check to triangle mesh construction to check for 0-based indexing

Triangle can output the mesh in 0 or 1-based indexing, but we can only
handle 1-based indexing. Previously using 1-based indexing gave a slightly
cryptic segfault.

Ideally oomph-lib should work with either index base but I don't know
enough about the code to implement the fix.
Added error check on files opened in tetgen mesh construction