add a gitdeps target to Makefile that checks out probert and curtin

This uses a silly python script to get the exact version that the
snapcraft.yaml specifies.

Makefile

@@ -3,7 +3,7 @@
 #
 NAME=subiquity
 PYTHONSRC=$(NAME)
-PYTHONPATH=$(shell pwd):$(shell pwd)/probert
+PYTHONPATH=$(shell pwd):$(shell pwd)/probert:$(shell pwd)/curtin
 PROBERTDIR=./probert
 PROBERT_REPO=https://github.com/canonical/probert
 DRYRUN?=--dry-run --bootloader uefi --machine-config examples/simple.json
@@ -25,7 +25,7 @@ install_deps:
 	sudo apt-get install -y python3-urwid python3-pyudev python3-nose python3-flake8 \
 		python3-yaml python3-coverage python3-dev pkg-config libnl-genl-3-dev \
 		libnl-route-3-dev python3-attr python3-distutils-extra python3-requests \
-		python3-requests-unixsocket python3-jsonschema python3-curtin python3-apport \
+		python3-requests-unixsocket python3-jsonschema python3-apport \
 		python3-bson xorriso isolinux python3-aiohttp probert cloud-init ssh-import-id
 
 i18n:
@@ -59,12 +59,17 @@ integration:
 
 check: unit integration
 
+curtin:
+	./scripts/checkout-part.py curtin
+
 probert:
 	@if [ ! -d "$(PROBERTDIR)" ]; then \
-		git clone -q $(PROBERT_REPO) $(PROBERTDIR); \
+		./scripts/checkout-part.py probert && \
 		(cd probert && $(PYTHON) setup.py build_ext -i); \
 	fi
 
+gitdeps: curtin probert
+
 schema: probert
 	@$(PYTHON) -m subiquity.cmd.schema > autoinstall-schema.json
 

scripts/checkout-part.py

@@ -0,0 +1,27 @@
+#!/usr/bin/python3
+import subprocess
+import sys
+import yaml
+
+part = sys.argv[1]
+
+
+def r(*args):
+    print('running', args)
+    subprocess.run(args, check=True)
+
+
+with open("snapcraft.yaml") as f:
+    config = yaml.safe_load(f)["parts"][part]
+
+r('git', 'clone', config['source'], part)
+
+
+c = None
+for k in "source-commit", "source-tag", "source-branch":
+    if k in config:
+        c = config[k]
+        break
+
+if c is not None:
+    r('git', '-c', 'advice.detachedHead=false', '-C', part, 'checkout', c)