Start adding a simple block_test

This is intended to be a functional test, not a performance one.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
block_test: check that writing and reading the initial sector works

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
block_test: check sector write/read at the beginning and the end

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
block_test: test some more combinations

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
block_test: ensure each sector has slightly different contents

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
block_tests: add some negative tests

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #15 from djs55/add-block-test

Add a set of block tests