refactor verify_flowstats and move to testutils

This needs to be centralized for later byte counter fuzzing changes.
refactor verify_portstats and move to testutils
refactor verify_queuestats and move to testutils
testutils: add 10% fuzz to byte counter matching

Some switches include the 4-byte Ethernet CRC in their counters. Since the spec
is ambiguous here we allow this and similar behavior by allowing the byte
counters to increment up to 10% more than we'd usually expect.