blockVolume: round up volume size for createVolume

The logical volume size granularity used in lvm(.py) is 1Mb, therefore
the size in sectors should be aligned. When the size is particularly
small this also prevents failing lvcreate calls with size 0m.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1009086
Change-Id: I5ae3d918ea4e7ca91383c3a3184a338cb40c4c27
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19390
Reviewed-by: Ayal Baron <abaron@redhat.com>