Summary:
This fixes two issues. One issue where the recent change of cdn to lookaside hostname broke our build download process. More about this can be found [here](https://fb.workplace.com/groups/flipperfyi/permalink/772986153467682/).
It also fixes a bug which occurred on a retry when an error happened. Recently I made changes where, if the build is downloaded then retrying shouldn't redownload it. But we used to remove the downloaded builds after install phase, so this diff just removes the build when the download is successfull.
Reviewed By: nikoant
Differential Revision: D23372251
fbshipit-source-id: b57e69f65a20fc123191962d60165a62859d4ef7
be641441d9