CLI: Return non-zero on unknown sub commands

[dnsmichi]

Tests

michi@mbpmif ~/dev/icinga/icinga2 (master *=) $ icinga2 sdfsdfsdf; echo "Status Code:$?"
[2019-05-07 12:40:54 +0200] critical/icinga-app: Command parsing error. Try '--help'.
Status Code:1
michi@mbpmif ~/dev/icinga/icinga2 (master *=) $ icinga2 daemon -C; echo "Status Code:$?"
[2019-05-07 12:41:08 +0200] information/cli: Icinga application loader (version: v2.10.4-643-gaa88271d5; debug)
[2019-05-07 12:41:08 +0200] information/cli: Loading configuration file(s).
[2019-05-07 12:41:08 +0200] information/ConfigItem: Committing config item(s).
[2019-05-07 12:41:08 +0200] information/ApiListener: My API identity: mbpmif.int.netways.de
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 2 Hosts.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 1 HostGroup.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 1 Endpoint.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 1 IcingaApplication.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 1 CheckerComponent.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 3 Zones.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 1 IdoMysqlConnection.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 1 NotificationComponent.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 1 ApiListener.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 7 CheckCommands.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 1 FileLogger.
[2019-05-07 12:41:08 +0200] information/ConfigItem: Instantiated 1 ApiUser.
[2019-05-07 12:41:08 +0200] information/ScriptGlobal: Dumping variables to file '/usr/local/icinga/icinga2/var/cache/icinga2/icinga2.vars'
[2019-05-07 12:41:08 +0200] information/cli: Finished validating the configuration file(s).
Status Code:0
michi@mbpmif ~/dev/icinga/icinga2 (master *=) $ icinga2 daemon --bumsti; echo "Status Code:$?"
[2019-05-07 12:41:22 +0200] critical/icinga-app: Error while parsing command-line options: unrecognised option '--bumsti'
Status Code:1

Auto-completion.

michi@mbpmif ~/dev/icinga/icinga2 (master *=) $ icinga2 daemon --
--close-stdio      --config           --define           --help             --log-level        --script-debugger  --version
--color            --daemonize        --errorlog         --include          --no-config        --validate
michi@mbpmif ~/dev/icinga/icinga2 (master *=) $ icinga2
api           ca            console       daemon        feature       node          object        pki           troubleshoot  variable

fixes #6585

[dnsmichi]

Unfortunately this breaks the way our CLI commands work. Reverted.