Consistent versions of root appear to be needlessly written multiple times

[vladimir-v-diaz]

write_metadata_file() was modified in PRs #379 and #383 to always write root.json and <version>.root.json if consistent snapshots = True. Given these changes, we should refactor the following lines: https://github.com/theupdateframework/tuf/blob/0ce016b7b19a0fc15443eed657a90246ec5df0aa/tuf/repository_lib.py#L213-L224

Log files and a closer inspection of this code show that multiple attempts are made to write root.json.

Thanks given to @FelixWang1994 for bringing this issue to our attention.

[vladimir-v-diaz]

This issue was fixed in #392 and #394

@FelixWang1994
Thanks for working on this issue.

[FelixWang1994]

My pleasure!