adding failing tests for fixnum args in an array.

The args need to be strings so that an error won't happen with `text.gsub` in https://github.com/mitchellh/vagrant/blob/bb052366f7f9616666299a97edcceadae007394a/plugins/provisioners/shell/provisioner.rb#L122

See my comments on mitchellh/vagrant#2982 as to why it needs to test for this.
change the shell provision config to make all the args strings

specifically arrays could contain `Fixnum` args and those wouldn't get turned into strings.
Merge pull request #4234 from b-dean/fixnum-array-args-fix

provisioner/shell: fix cannot handle Fixnum array args