Fix a "bug" in the storage pool test driver code which "assumed"
testStoragePoolObjSetDefaults should fill in the configFile for
both the Define/Create (persistent) and CreateXML (transient) pools
by just VIR_FREE()'ing it during CreateXML.  Because the configFile
was filled in, during Destroy the pool wouldn't be free'd which
could cause issues for future patches which add tests to validate
vHBA creation for the storage pool using the same name.