Changes to processing options for `**fs.xtreemfs` commands, should fix issue #5

 * changed processing of options
 * fix for passing `undef` value for options without parameters
 * changed unit tests to accomodate changes
 * added more acceptance tests with more complex options, like in issue #5
Merge branch 'develop' of github.com:wavesoftware/puppet-xtreemfs into develop