PEP8 fixes in run_tests.py
PEP8 fixes in run_tests.py

mit-crpg/openmc,smharper/openmc,mit-crpg/openmc,paulromano/openmc,amandalund/openmc,shikhar413/openmc,walshjon/openmc,smharper/openmc,liangjg/openmc,amandalund/openmc,johnnyliu27/openmc,wbinventor/openmc,amandalund/openmc,paulromano/openmc,liangjg/openmc,wbinventor/openmc,walshjon/openmc,liangjg/openmc,johnnyliu27/openmc,mit-crpg/openmc,shikhar413/openmc,johnnyliu27/openmc,smharper/openmc,shikhar413/openmc,mit-crpg/openmc,wbinventor/openmc,wbinventor/openmc,walshjon/openmc,amandalund/openmc,paulromano/openmc,shikhar413/openmc,walshjon/openmc,johnnyliu27/openmc,paulromano/openmc,liangjg/openmc,smharper/openmc