Surround keytool path with double quotes (closes #3)

This PR surrounds the keytool command path with doubles quotes when running on Windows platform.

Two helper methods are added at the end of the provider to build the java_home and keytool paths.

The PR also includes the following changes:
 * remove `directory "#{Chef::Config[:file_cache_path]}"}}}` resource declarations, as they are not necessary (I assume this directory always exists) and they generate warnings (resource cloning)
 * replace calls to `node['java']['java_home']` by the `java_home` variable