In #36 some of the odd errors were due to seeks beyond the end of the
disc. This was because the disc was "specially crafted" to be 25GB + 1
byte, which doesn't fit into the normal 512 byte sectors expected of a
disc. This lead to reads going beyond the end of the disc etc.
If a similarly evil disc is used with `losetup`, it just ignores the
last bytes of the disc that don't fit into 512 chunks. This is what
that patch does, logging an error at the same time.
Previously the proxy would just disconnect when it saw an NBD protocol
error, and retry the operation it was in the middle of.
Additionally, the server needs to return the correct error types when
this happens.
This number is peppered all over the test suite, so changing @blocksize
for everything is not a goer, when we really only need to change it for
one test.
This is a bit of a cheat really, but `#read` returns an ASCII encoded
string, where as our ruby generates UTF-8 encoded strings, causing
assertion failures.
Fixes#20
