Attempting to migrate a file between pools with "lfs migrate" fails when only the poolname is specified, without any other stripe options.

E.g. this doesn't work:

lfs migrate -p pool2 /lustre/dir0/file0

but this does work:

lfs migrate -c 1 -p pool2 /lustre/dir0/file0

The issue seems to have been introduced in LU-11510; reverting the commit from that ticket addresses the issue.