Dockerfile's COPY directive only copies the contents of a directory when
src is a directory. It does not copy the directory itself. This meant
the copy we were using to copy static files put them in /var/gerrit and
not /var/gerrit/static where we need them to be.
Update the Dockerfile to copy to /var/gerrit/static/ to fix this and add
some resource fetching tests to ensure they are served correctly.
Change-Id: I3bb4c06f3d7a57dcfccbbdb27cb8405586949949
7df09ecef5