refactor FileResource.inputStream to be easier to use #2271
for any client code which needs to convert a uri-like path to an inputstream
the motivation for this PR comes from jruby-openssl-0.9.6.dev:
from the user there comes a String with path to a PEM resource. as it turns out this path can be any uri-like path (like from rubygems: https://github.com/jruby/jruby/blob/master/lib/ruby/stdlib/rubygems/request.rb#L42).
the following boilerplate code to convert a uri-like path into an input-stream:
this PR cleans up the API for such "conversion" and to release jruby-openssl with this clean API it needs a released jruby version with this PR merged.
for any client code which needs to convert a uri-like path to an inputstream the way to go is ```JRubyFile.create(runtime, path).inputStream()```