Ensures that external resources are not exported by default.

[dbernstein]

Users must now specify --external=true to export proxied and redirected external resources.

Resolves: https://jira.lyrasis.org/browse/FCREPO-3416

This PR is covered by new integration test.

To test manually:

1. start up fcrepo 5.1.1 with allowed external content

cat "https://" > allowed_external_paths.txt
java -Dfcrepo.external.content.allowed=./allowed_external_paths.txt -jar fcrepo-webapp-5.1.1-jetty-console.jar --headless

2. create a proxied resource pointing at the newly created binary.

curl -i -H"Link: <https://wiki.lyrasis.org/download/attachments/4980737/atl.site.logo>; rel=\"http://fedoraent\"; handling=\"proxy\"; type=\"image/png\"" -XPUT -ufedoraAdmin:fedoraAdmin http://localhost:8080/rest/proxy_test

4. perform an export

 java -jar fcrepo-import-export-1.1.0-SNAPSHOT.jar -b -d export-3416 -u fedoraAdmin:fedoraAdmin  -b -m export -r http://localhost:8080/rest

5. verify that the external resource file is zero length

ls -lastR export-3416/ | grep proxy_test.external

6. perform export again with --external flag enabled

# remove previous export
 rm -rf export-3416
# run export
 java -jar target/fcrepo-import-export-1.1.0-SNAPSHOT.jar -b -d export-3416 -u fedoraAdmin:fedoraAdmin  -b --external -m export -r http://localhost:8080/rest

7. verify that the external resource non-zero length.

ls -lastR export-3416/ | grep proxy_test.external

[awoods]

Works as advertised. Should be good to go, pending response to code review comments.

[awoods]

I am not seeing this InputStream being closed anywhere. Is it happening?

[awoods]

For completeness, may as well add another test for proxy.