Should tell user when baseurl is invalid

[bseeger]

When the user enters an invalid base url, unless the test suite is unable to connect to it, the user has no indication that they've entered something incorrectly.

Ie, it looks like the test suite runs just fine when one does this:

java -jar testsuite-1.0-SNAPSHOT-shaded.java -b http://localhost:8080

But that path is incorrect and needed /fcrepo4/rest to actually reach the end point.

There's a stack trace when the system cannot connect to a server, but there's no failure feedback when the url is just slightly wrong.