elasticsearch-croneval shouldn't dump a stacktrace for invalid patterns

[pugnascotia]

Elasticsearch version

7.4.2, master

Description of the problem including expected versus actual behavior:

When elasticsearch-croneval is run with a malformed cron pattern, it dumps a stacktrace to the terminal.

The tool ought to simply report that the pattern is malformed and either direct the user to the documentation or print a brief summary of the expected input (I'd vote for the latter).

Steps to reproduce:

1. `bin/elasticsearch-croneval "*"

[elasticmachine]

Pinging @elastic/es-core-features (:Core/Features/Watcher)

[gaobinlong]

Hi @pugnascotia , this issue can be closed as the related PR #49744 has been merged.