Import bucket metadata must show CORS and general errors if any are found

Community Contribution License

All community contributions in this pull request are licensed to the project maintainers under the terms of the Apache 2 license. By creating this pull request I represent that I have the right to license the contributions to the project maintainers under the Apache 2 license.

Description

Fix a bug where any error on the zip file itself (rather than a specific bucket) was not reported, e.g. malformed directory.
Report whether CORS bucket settings were imported successfully

Motivation and Context

How to test this PR?

Example of failed import errors, with this PR:

0/2 buckets were imported successfully.
Errors:

Name      : BADFORMAT/corsexporttest/cors.xml
  Error:  malformed zip - expecting format bucket/<config.json>

Name      : corsexporttest
  Notification:  ✔
  Quota:  ✔
  CORS:  ✗

Types of changes

[x] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Optimization (provides speedup with no functional changes)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[ ] Fixes a regression (If yes, please add commit-id or PR # here)
[ ] Unit tests added/updated
[ ] Internal documentation updated
[ ] Create a documentation update request here

minio / mc