component/nginx: make nginx-push-stream not shared

This part was wrongly inheriting from nginx, but it should inherit from
nginx-common instead, so that it is not shared, because as it installs from a
git clone we can not share it.

It would be possible to make it shared by downloading a git archive and using
a dummy slapos.recipe.cmmi recipe for nginx-push-stream-module parts, so that
it is also shared, but since nothing depends on nginx and it is small, that
does not seem to be worth it.

component/nginx/buildout.cfg

@@ -85,7 +85,7 @@ revision = 3d3a204177d3a7ab8a2858e04e792a6d11bf133f
 git-executable = ${git:location}/bin/git
 
 [nginx-push-stream]
-<= nginx
+<= nginx-common
 configure-options=
   --with-ipv6
   --with-http_ssl_module