Progress indicator: Show on what machine we're building

E.g.

  $ nix build nixpkgs.hello --builders 'root@wendy'
  [1/0/1 built] building hello-2.10 on ssh://root@wendy: checking for minix/config.h... no

1 files changed, 1 insertions, 1 deletions

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index 92ae99e16..d2fac09f8 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -196,7 +196,7 @@ int main (int argc, char * * argv)
         }
 
 connected:
-        std::cerr << "# accept\n";
+        std::cerr << "# accept\n" << storeUri << "\n";
 
         auto inputs = readStrings<PathSet>(source);
         auto outputs = readStrings<PathSet>(source);