Manage: allow adding device that is just large enough to v1.x array.

Manage: allow adding device that is just large enough to v1.x array.

When adding a device to an array, we check that it is large enough.

Currently the check makes sure there is also room for a reasonably
sized bitmap.  But if the array doesn't have a bitmap, then this test
might be too restrictive.
So when adding, only insist there is enough space for the current
bitmap.
When Creating, still require room for the standard sized bitmap.

This resolved Debian Bug 500309