Got the tests working with travis.

Noticed some problems with expected return values for the cases in which
the given resource didn't exist. Now it returns 404 if the resource is
missing before doing the permission checks and returning a 401 or 403.

The reason behind this, is the resource needs to fetched before calling the
islandora access_hooks. Which determine the users access.

Also updated the README so that the default policies used by islandora_tomcat
are the same the user is instructed to remove and use.
Travis was failing in 3.5 because there is a bug in fedora 3.5 that prevents
modification of the DC datastream.

Changed the test to test the MODS datastream instead so it will pass on 3.5.

See the converation here:
http://fedora-commons.1317035.n2.nabble.com/fcrepo-user-REST-API-modifyDatastream-on-DC-fails-with-InputStream-cannot-be-null-td7436589.html
Merge pull request #2 from nigelgbanks/7.x-travis-policy-assumption-fix

Hopefully this will fix Travis :)