Delete default volume size 100M in drivers

There is check: if volume size == 0 we set default value to 100M,
it uses only in tests and it's little bit confusing.Use code only
for tests in drivers is bad practice.

Also the create volume flow already won't let user to create
a volume  with size 0. So it was decided to remove this check.

Change-Id: I620ae8fff4634c60a02329f22d1a0343b27aa955
Merge "Delete default volume size 100M in drivers"