Helper handles error in creation of TransportFactory

In case the EtchTransportFactory cannot return a ServerFactory for the
given URI, e.g. in case the user forgets to add the tcp:// prefix in the
connection URI, now an error is returned.

Change-Id: I636d2e6a507210fa371b73dd380a0e6ed15cef3b

git-svn-id: https://svn.apache.org/repos/asf/etch/trunk@1584587 13f79535-47bb-0310-9956-ffa450edef68