Update obsys_rc.py and check_obsysrc.py to Python 3

[gmao-jstassi]

in the GMAO_etc directory, plus updates to the unittests files associated with these scripts.

Also, some unrelated updates to cmpdir.pl to

• allow users to toggle between diff and xxdiff when comparing files
• add -B (ignore blank lines) to -bwi flags when ignoring trivial differences between files