Revert "modify MeshSymmetryErrorHandler to reflect behavior of other non-monitor handlers. If the vasprun.xml cannot be parsed (The job did not complete successfully) the handler will hit the except, pass, and return False. Otherwise, if the run did not converge, or ISYM=0, the handler will check vasp.out for the error message"

This reverts commit 88d2e8b7d24cda90137096cc9b6a81f8a3f8c7c9.

It broke things
Add unparsable vasprun.xml to test_files
(So MeshSymmetryErrorHandler test works -- we want it to catch when vasp
dosn't write a valid xml))
Merge branch 'master' of github.com:materialsproject/custodian