Matrix properties should be CGI escaped

`URI.escape` has been deprecated: http://stackoverflow.com/a/2832003

Furthermore URI.escape and does not properly encode things like plus signs (`+`) which should be turned into a `%2B` while actual spaces should be turned into a `+`!

I noticed this bug when examining a matrix property for a build version. The original build version was: 
`12.0.0-alpha.1+20140826080510.git.50.f5ff271` 
but Artifactory had stored it as: 
`12.0.0-alpha.1 20140826080510.git.50.f5ff271`!

/cc @opscode/release-engineers