Clarify exit status code

When there is a CLI error in Click arguments, the exit status code is set to 2. When we are reporting a CLI issue with message_exit() we returns 1.

Following sources are not agree on 1 and 2:

• https://tldp.org/LDP/abs/html/exitcodes.html
• https://jazz.net/help-dev/clm/topic/com.ibm.team.scm.doc/topics/r_scm_cli_retcodes.html

See tests/test_tx.py:test_tx_passed_amount_cli()