conf: Check for storage conflicts across pool types

conf: Check for storage conflicts across pool types

https://bugzilla.redhat.com/show_bug.cgi?id=1233129

The virStoragePoolObjSourceFindDuplicate logic used by PoolCreateXML
and PoolDefineXML avoids comparing the new definition against "other"
pool types. This can cause unexpected corruption if two different pool
source types used the same source device path. For example, a 'disk'
pool using source type device=/dev/sdc could be unwittingly overwritten
by using /dev/sdc for a 'logical' pool which also uses the source
device path.

So rather than blindly ignoring those checks when def->type !=
pool->def->type - have the pool->def->type switch logic handle the
check for which def->type's should be checked.