[shongo-cli] create-tag command loops on failure

[Puckoland]

When creating a new tag using shongo-cli, it may fail (e.g. using the same name as was already present in the tag table).
This results in CLI looping - trying to create a specified tag and failing repeatedly.

Sample CLI output of creating tag t5 which is already defined.

shongo> create-tag 
Tag name: t5
Creating tag...
[ERROR] Server failed to perform request!
Fault 0: Unknown error: Failed to invoke Resource.createTag: Error while committing the transaction
Creating tag...
[ERROR] Server failed to perform request!
Fault 0: Unknown error: Failed to invoke Resource.createTag: Error while committing the transaction
Creating tag...
[ERROR] Server failed to perform request!
Fault 0: Unknown error: Failed to invoke Resource.createTag: Error while committing the transaction
...

Shongo-controller log:

Caused by: org.postgresql.util.PSQLException: ERROR: duplicate key value violates unique constraint "tag_name_key"
  Detail: Key (name)=(t5) already exists.