spec: Don't try to rebuild webpack when building released tarballs

Release tarballs already have dist/. We can't rebuild the webpack in an
RPM as that requires npm and network access for `npm install`. But we
also don't want to ship the entire `node_modules/` as that is huge and
would require lots of careful license review.

So ship a stub node_modules/ that satisfies the Makefile dependency.
Make sure that this is not newer than package.json or anything in dist/,
so that none of the Makefile's rebuild rules trigger.

Closes #36

cockpit-starter-kit.spec.in

@@ -17,7 +17,7 @@ Cockpit Starter Kit Example Module
 %setup -n cockpit-starter-kit
 
 %build
-make
+# There is nothing to do, release tarballs already have dist/.
 
 %install
 make install DESTDIR=%{buildroot}