import_export protected branches not honoured
### Summary
When importing a project into a new EE instance, the protected branches are not set correctly causing no-one to have permission to push.
### Steps to reproduce
1) Export a project with protected branches.
2) Import the project into a new instance
3) Observer that the protected branches now have 0 roles or users
### Expected behavior
Should continue to observe the original protected branches

### Actual behavior
Does not include the correct roles or users

The current work around is to manually set the permissions after the import.
#### Results of GitLab environment info
GitLab Enterprise Edition 8.16.1-ee 060f824
issue