Correct InvalidInstanceID.NotFound test.

* exercises/euca.sh: The match filtering InvalidInstanceID.NotFound
is cleaned up to eliminate numerous leaning toothpicks, and now also
actually works. The previous version was incorporating literal
square brackets into the pattern where I think a character list
match may have been intended instead, but was not actually necessary
anyway.

Change-Id: I765a20000e7b6ba6deadce8cad3bbc9559fcdd0d
Merge "Correct InvalidInstanceID.NotFound test."