Ignore various huge directories from docker builds

None of these should be part of an image build; they just get mounted in
as needed.  For IIP testing we really don't want to keep sending gigs of
data to the docker daemon.

.dockerignore

@@ -2,3 +2,7 @@
 set_content
 jetty
 *.sqlite3
+batch
+media
+tmp
+log