Adding a check for dagmc when exporting an OpenMC model.
Adding a check for dagmc when exporting an OpenMC model.

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