workaround zfs create -V error for unaligned sizes

fixes the 'cannot create 'nvme/foo': volume size must be a multiple of
volume block size' error by always rounding the size up to the next 1M
boundary. this is a workaround until
https://github.com/zfsonlinux/zfs/issues/8541 is solved.
the current manpage says 128k is the maximum blocksize, but a local test
showed that values up to 1M are allowed. it might be possible to
increase it even further (see f1512ee61).

Signed-off-by: Mira Limbeck <m.limbeck@proxmox.com>

PVE/Storage/ZFSPoolPlugin.pm

@@ -309,7 +309,12 @@ sub zfs_get_pool_stats {
 
 sub zfs_create_zvol {
     my ($class, $scfg, $zvol, $size) = @_;
-    
+
+    # always align size to 1M as workaround until
+    # https://github.com/zfsonlinux/zfs/issues/8541 is solved
+    my $padding = (1024 - $size % 1024) % 1024;
+    $size = $size + $padding;
+
     my $cmd = ['create'];
 
     push @$cmd, '-s' if $scfg->{sparse};