verdi migrate: make --in-place work across different file systems (…

…#4393)

The `verdi migrate` command assumed implicitly that the archive that is
to be migrated, resides on the same file system as the one that is used
by the `tempfile` module. If this is not the case, the `os.rename` call
used to atomically move the migrated archive to the original will fail
with the exception:

    OSError: [Errno 18] Invalid cross-device link

Changing `os.rename` to `shutil.move` fixes this problem. The downside,
however, is that the move is no longer atomic, but that is probably why
`os.rename` is restricted to same filysystem operations.

aiida/cmdline/commands/cmd_export.py

@@ -11,6 +11,7 @@
 """`verdi export` command."""
 import os
 import tempfile
+import shutil
 
 import click
 import tabulate
@@ -245,7 +246,7 @@ def migrate(input_file, output_file, force, silent, in_place, archive_format, ve
                 archive.add(folder.abspath, arcname='')
 
         if in_place:
-            os.rename(output_file, input_file)
+            shutil.move(output_file, input_file)
             tempdir.cleanup()
 
         if not silent: