avoid javax.script.ScriptException

fix for issue https://github.com/sapnwcloudlabs/nwcloud-maven-plugin/issues/2

With the fix, the nwcloud goals obviously are failing  as well, but the output is nicer than the exception raised without the fix:

[INFO] [INFO]
[INFO] [INFO] --- nwcloud-maven-plugin:1.0.1.RELEASE:stop (after.deploy) @ runciter ---
[INFO]
[INFO] init:
[INFO]
[INFO] password:
[INFO] [INFO] Trying to automatically retrieve password from servers defined in Maven's 'settings.xml'.
[INFO] [INFO]  - No matching server found, or matching server(s) had no password specified.
[INFO]
[INFO] stop:
[INFO]      [java]
[INFO]      [java] Requesting stop for:
[INFO]      [java]    application: dev
[INFO]      [java]    account    : myos
[INFO]      [java]    host       : https://prod.jpaas.sapbydesign.com
[INFO]      [java]    synchronous: true
[INFO]      [java]    SDK version: 2.0.5
[INFO]      [java]    user       : i051108
[INFO]      [java]
[INFO]      [java]
[INFO]      [java] Stop request finished with error !
[INFO]      [java] Authentication failed. Check if you have a valid user authorized to perform the current operation in the provided account and make sure the account name is spelled correctly
[INFO]      [java] Component status: UNKNOWN
[INFO]      [java]
[INFO]      [java] Failed to execute command [stop]
[INFO]      [java] Java Result: 136
[INFO] [INFO]
[INFO] [INFO] --- nwcloud-maven-plugin:1.0.1.RELEASE:deploy (after.deploy) @ runciter ---
[INFO]