Volume detection in the scsi backend was duplicating code already
present in storage_backend.c. Let's drop the duplicate code.
Also, change the shared function name to be less generic, and remove
some error squashing in the other call site.
We were squashing error messages in a few cases. Recode to follow common
ret = -1 convention.
v2: Handle more error squashing issues further up in MakeNewVol and
CreateVols. Use ret = -1 convention in MakeVols.
* src/storage/storage_backend_mpath.c (virStorageBackendIsMultipath):
The result of dm_get_next_target was never used (and isn't needed),
so don't store it.
The virConnectPtr is no longer required for error reporting since
that is recorded in a thread local. Remove use of virConnectPtr
from all APIs in storage_conf.{h,c} and storage_encryption_conf.{h,c}
and update all callers to match
