Use better `raise` syntax to suppress compatibility warnings.

Ruby Enterprise (ruby 1.8.7 (2009-06-12 patchlevel 174) [x86_64-linux], MBARI 0x6770, Ruby Enterprise Edition 2009.10) complains about the `raise` lines in the java_ks provider:

    /var/lib/puppet/lib/puppet/provider/java_ks/keytool.rb:130: warning: parenthesize argument(s) for future version

Adding a comma here suppresses the warning and seems to be more in line with Ruby community conventions.

(Neither version of this change cause problems in 1.8.9.)