deltas: Expose the filename parameter

The C API (ostree_repo_static_delta_generate) knows what to do
with it, but this parameter was never exposed via command line
tool.

Closes: https://github.com/ostreedev/ostree/issues/695

Closes: #703
Approved by: jlebon

tests/test-delta.sh

@@ -121,6 +121,14 @@ if ${CMD_PREFIX} ostree --repo=repo static-delta generate --from=${origrev} --to
     assert_not_reached "static-delta generate --from=${origrev} --empty unexpectedly succeeded"
 fi
 
+${CMD_PREFIX} ostree --repo=temp-repo init --mode=archive
+${CMD_PREFIX} ostree --repo=temp-repo pull-local repo
+${CMD_PREFIX} ostree --repo=temp-repo static-delta generate --empty --to=${newrev} --filename=some.delta
+assert_has_file some.delta
+${CMD_PREFIX} ostree --repo=temp-repo static-delta list > delta-list.txt
+assert_file_has_content delta-list.txt 'No static deltas'
+rm temp-repo -rf
+
 echo 'ok generate'
 
 ${CMD_PREFIX} ostree --repo=repo static-delta show ${origrev}-${newrev} > show.txt