Before this patch, if we booted a node just after removing
a different node, the booting node may still see the removed node
as NORMAL and wait for it to be UP, which would time out and fail
the bootstrap.
This issue caused scylladb/scylladb#17526.
Fix it by recalculating the nodes to wait for in every step of the
`wait_alive` loop.
The original patch merged to master,
017134fd38, differs because
the conflicting patch, e4c3c07510,
hasn't been backported to 5.4. However, we don't have to
additionally backport that patch. These changes are orthogonal.
193fda6dfb