The sparsify function can be used to make an image sparse by replacing
runs of zeros with holes. This change adds a wrapper for the basic
rbd_sparsify function and accompanying tests.
Signed-off-by: John Mulligan <jmulligan@redhat.com>
A previous change improved our use of pointers such that go vet no
longer had an issue with these lines but if we ever need to change the
interaction between rbd and rados like that again we can now rely on a
single call site `cephIoctx` that will return our ceph/c type given the
public Go-language level type from the rados pkg.
Signed-off-by: John Mulligan <jmulligan@redhat.com>