drop non-I/O threading in upgrade
drop non-I/O threading in upgrade

threading does nothing in python unless the task is heavily
I/O-dependent. we already use threads to retrieve data so we
really shouldn't wrap entire upgrade step in threading as it doesn't
offer any benefits.

Partial-Bug: #1600796
Change-Id: Ia4e834e6566cf053b9f26b2bee9142dff0c72444

gnocchixyz/gnocchi,leandroreox/gnocchi,sileht/gnocchi,sileht/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi