When run glossary-delete by user that does not have glossary-admin role, 
It should return "You are not a glossary-admin" instead of misleading 
"Incorrect usnername/password"

Version-Release number of selected component (if applicable):
Server: Zanata 3.6.0-SNAPSHOT (git-server-3.5.1-152-g3b2474e)
Client: org.zanata:zanata-maven-plugin:3.4.1:glossary-delete (default-cli)

Steps to Reproduce: 
1.  Set ZANATA_USERNAME to a user that is not a glossary-admin
2.  mvn -e org.zanata:zanata-maven-plugin:glossary-delete  -Dzanata.url=$ZANATA_URL -Dzanata.username=$ZANATA_USERNAME Dzanata.key=$ZANATA_KEY  -Dzanata.lang=$ZANATA_LANG
 

Actual:
[ERROR] Failed to execute goal org.zanata:zanata-maven-plugin:3.4.1:glossary-delete (default-cli) on project standalone-pom: Zanata mojo exception: Incorrect username/password -> [Help 1]

Expected:
[ERROR] Failed to execute goal org.zanata:zanata-maven-plugin:3.4.1:glossary-delete (default-cli) on project standalone-pom: Zanata mojo exception: You are not a glossary-admin -> [Help 1]