This introduces strtosz_suffix() which allows the caller to specify a
default suffix in case the non default of MB is wanted.

strtosz() is kept as a wrapper for strtosz_suffix() which keeps it's
current default of MB.
Signed-off-by: NJes Sorensen <Jes.Sorensen@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>