Fix benchmark

- Disable compression so we get realistic push numbers.
- Don't use /dev/null on push since we encountered this error:
('/dev/null': remote fchown() failed uid: 0 gid: 0: Permission denied)
- Enable device dd benchmark
- Refactor so we can pick size of all push on a single line.

Fixes: 360943277
Fixes: 360934966
Test: This is it
Change-Id: I65c169ea93867a6edc62ca09c6da4640f4d169bb
2 files changed