Relaxing error message comparison so that test passes against MongoDB 2.6

MongoDB 2.6 is returning an error message starting with:

"Insert list failed: insertDocument :: caused by :: "

which was making this test fail.

Note also that to test against MongoDB 2.6.0-rc2 I had to in the setup method first strip the "-rc2" from the version before passing it to Spring's Version class, which doesn't handle anything but integer versions.