build: add Ropsten derivations for arvo and pills

Arvo testnets typically use Ropsten's deploy of the Azimuth contract
instead of mainnet's.  This commit adds an 'arvo-ropsten' derivation for
Arvo as specialised to Ropsten.

In addition to using a different Azimuth address in %zuse, this also
configures %ames and :acme appropriately for running an alternate
network on Ropsten.  %ames has its protocol version incremented, and
:acme uses the Let's Encrypt staging API.

Included here are derivations for creating brass and ivory pills using
arvo-ropsten, to boot.

nix/ops/default.nix

@@ -2,10 +2,11 @@
 
 let
 
-  tlon  = import ../pkgs { inherit pkgs; };
-  arvo  = tlon.arvo;
-  herb  = tlon.herb;
-  urbit = if debug then tlon.urbit-debug else tlon.urbit;
+  tlon         = import ../pkgs { inherit pkgs; };
+  arvo         = tlon.arvo;
+  arvo-ropsten = tlon.arvo-ropsten;
+  herb         = tlon.herb;
+  urbit        = if debug then tlon.urbit-debug else tlon.urbit;
 
   bootbrass = ../../bin/brass.pill;
   bootsolid = ../../bin/solid.pill;
@@ -17,6 +18,13 @@ let
     arvo = null;
   };
 
+  ropzod = import ./fakeship {
+    inherit pkgs herb urbit;
+    pill = bootsolid;
+    ship = "zod";
+    arvo = arvo-ropsten;
+  };
+
   zod = import ./fakeship {
     inherit pkgs herb urbit arvo;
     pill = bootsolid;
@@ -48,11 +56,23 @@ rec {
     pier = zod;
   };
 
+  brass-ropsten = import ./brass {
+    inherit pkgs herb urbit;
+    arvo = arvo-ropsten;
+    pier = ropzod;
+  };
+
   ivory = import ./ivory {
     inherit pkgs herb urbit arvo;
     pier = zod;
   };
 
+  ivory-ropsten = import ./ivory {
+    inherit pkgs herb urbit;
+    arvo = arvo-ropsten;
+    pier = ropzod;
+  };
+
   image = import ./image {
     inherit pkgs urbit;
     pill = bootsolid;

nix/pkgs/arvo-ropsten/builder.sh

@@ -0,0 +1,26 @@
+source $stdenv/setup
+
+cp -r $src tmp
+chmod -R u+w tmp
+
+ZUSE=tmp/sys/zuse.hoon
+AMES=tmp/sys/vane/ames.hoon
+ACME=tmp/app/acme.hoon
+
+# replace the mainnet azimuth contract with the ropsten contract
+sed --in-place \
+  's/\(\+\+  contracts  \)mainnet\-contracts/\1ropsten-contracts/' \
+  $ZUSE
+
+# increment the %ames protocol version
+sed -r --in-place \
+  's/^(=\+  protocol\-version=)([0-9])/echo "\1$(echo "(\2+1) % 8" | bc)"/e' \
+  $AMES
+
+# use the staging API in :acme
+sed --in-place \
+  's_https://acme-v02.api.letsencrypt.org/directory_https://acme-staging-v02.api.letsencrypt.org/directory_' \
+  $ACME
+
+cp -r tmp $out
+chmod -R u+w $out

nix/pkgs/arvo-ropsten/default.nix

@@ -0,0 +1,8 @@
+{ pkgs }:
+
+pkgs.stdenv.mkDerivation {
+  name = "arvo-ropsten";
+  buildInputs = [ pkgs.bc ];
+  builder = ./builder.sh;
+  src = pkgs.buildRustCrateHelpers.exclude [ ".git" ] ../../../pkg/arvo;
+}

nix/pkgs/default.nix

@@ -6,6 +6,7 @@ let
 
   ent          = import ./ent          { inherit pkgs; };
   arvo         = import ./arvo         { inherit pkgs; };
+  arvo-ropsten = import ./arvo-ropsten { inherit pkgs; };
   herb         = import ../../pkg/herb { inherit pkgs; };
 
   ge-additions = import ./ge-additions {
@@ -25,4 +26,4 @@ let
 
 in
 
-{ inherit ent ge-additions arvo herb urbit urbit-debug; }
+{ inherit ent ge-additions arvo arvo-ropsten herb urbit urbit-debug; }