Improve error-handling for `java.net.URL` deserialization

[cowtowncoder]

(for background see dropwizard/dropwizard#1647)

Currently exception from construction of java.net.URI is not explictly handled but bubbles up and probably ends in generic wrapper, instead of more semantically meaningful message.
We should handle that explicitly to handle it better, to allow for more graceful handling at higher level.

[cowtowncoder]

Looks like failure with an invalid URI (like one containing space character) does throw InvalidFormatException as expected.

[cowtowncoder]

Ah! But handling of java.net.URL did NOT catch it -- fixing.