With Angular CLI version 8, migrations cannot be re-run with the
`--migrate-only` flag as there was a recent regression introduced
in e406f00909 (diff-0d0a748fb9a38a7ccde08d9b42e70bce) as it now passes
a normalized platform path to the `engine.createCollection` call.
This breaks as there is incorrect logic within
`node-modules-engine-host` that causes the schematic collection to be
searched within the `package.json#schematics` entry. This is incorrect
as migration schematics specify their migration schematics in a separate
schematic collection file which is part of `package.json#ng-update`.
Fixes#14565
