BmapCreate: implement arbitrary hash type support

BmapCreate: implement arbitrary hash type support

Instead of just supporting SHA1 hash functions type, support arbitrary hash
function type. Well, actually "arbitrary" means any hash function supported by
the "hashlib" python module.

In particular, we are interested to switch from SHA1 to SHA256.

Unfortunately, this is a format change, since format version 1.3 guaranteed
that checksum is always SHA1. This is why this patch also increases the format
version to 1.4.

Change-Id: I096b47d6e4a413368d42e40ce8ebb06f612619c5
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>