better error when object was not found remotely

creates an erro message that uses channel device name as well as path
makes more sense for devices/channels that do not have a path
refactor ClusterController

move some methods of ClusterController into ClusterConfigParser
the methods that depend only on data from parser should be in parser
added ability to use POST data as channel input

using `X-Zerovm-Source` header clients can now attach a POST request payload to a job (even clustered one)
docs updated
Merge pull request #101 from pkit/open

added ability to use POST data as channel input