Description of problem:
When a non-maintainer put-project or put-version on an existing project,
the expected behavior should show error message  "User xxx is not a maintainer" error status 403.

However, Zanata showed error message "Invalid username/password" (Error status 401), which is misleading.



Version-Release number of selected component (if applicable):
Zanata 3.6.0-SNAPSHOT (git-server-3.5.1-152-g3b2474e) |

How reproducible:
Always

Steps to Reproduce:
1. Find a existing project
2. Run following with a user who is neither maintainer nor admin
mvn -B -e org.zanata:zanata-maven-plugin:put-version -Dzanata.versionProject=$PROJECT_SLUG -Dzanata.versionSlug=$VERSION_SLUG

Actual results:
[ERROR] Failed to execute goal org.zanata:zanata-maven-plugin:3.4.1:put-version (default-cli) on project standalone-pom: Zanata mojo exception: Incorrect username/password -> [Help1] 

Expected results:
[ERROR] Failed to execute goal org.zanata:zanata-maven-plugin:3.4.1:put-version (default-cli) on project standalone-pom: Zanata mojo exception: User xxx is not the maintainer -> [Help1]