Add IO test for q, aux and gauges (related to issues #111 and #42)

Test for ascii and petsc io routine that includes verifying q, aux, gauges that are written in files.
I've added the method get_aux_global analogous to  get_q_global.

This pull request is rebased on pull request #227 (because I needed some fixes from there). If this one was merged, no need to merge pull request #227