Disentangle ProxyRepoDownloadTest from RepoDownloadTest

Turns out that the Proxy test only worked because the RepoDownloadTest
had already downloaded the test app and therefore it never actually
hit the proxy server. If it did, it would have noticed that it tried
to hit it with a relative url first (because localhost:9193 is in the
list of repo resolvers) and then tried a wrong url (ending in :9193,
not in :9192).

Run the proxy on another port (9194), fix the request URI using 9193,
change the name of the proxy app to not be the same as the non-proxy
download app.

Both ProxyRepoDownloadTest and RepoDownloadTest are still stateful
tests because if they are run multiple times without cleaning out the
mod-test folder, the test will not hit the actual server the second
and any further time.
Fix StringIndexOutOfBoundsException if UriParser.path(...) was used on a request that contains no path
Make sure findLoadedClass is called, also allow for serialization of platform blocking actions
Merge branch 'master' of github.com:eclipse/vert.x
Merge pull request #765 from hgschmie/download-fix

Disentangle ProxyRepoDownloadTest from RepoDownloadTest
Better error message when JAVA_HOME is not set
Make JsonElement serializable
use createNew as javadoc requires
allow users to put resources into a platform_lib directory in their module for fatjars - this will be added to the platform classpath
Merge branch 'master' of github.com:eclipse/vert.x
increaase timeout to avoid failures on CI