Allow passing an arbitrary package list to assemble

This lets you build an image to install a package or set of packages
without having to build a fake pbr install.

Change-Id: I6c171881283b89a14a532f31aedb33e223a0ea1f

docker/python-builder/scripts/assemble

@@ -73,6 +73,8 @@ function install_wheels {
     done
 }
 
+PACKAGES=$*
+
 # bindep the main package
 install_bindep
 
@@ -83,17 +85,25 @@ for sibling in ${ZUUL_SIBLINGS:-}; do
     popd
 done
 
-# pbr needs git installed, else nothing will work. Do this in between
-# bindep and wheel so that we don't miss git in target images.
-apt-get install -y git
-
 # Use a clean virtualenv for install steps to prevent things from the
 # current environment making us not build a wheel.
 python -m venv /tmp/venv
 /tmp/venv/bin/pip install -U pip wheel
 
-# Install the main package
-install_wheels
+# If we got a list of packages, install them, otherwise install the
+# main package.
+if [[ $PACKAGES ]] ; then
+    /tmp/venv/bin/pip install --cache-dir=/output/wheels $PACKAGES
+    for package in $PACKAGES ; do
+      echo "$package" >> /output/packages.txt
+    done
+else
+    # pbr needs git installed, else nothing will work. Do this in between
+    # bindep and wheel so that we don't miss git in target images.
+    apt-get install -y git
+
+    install_wheels
+fi
 
 # go through ZUUL_SIBLINGS, if any, and build those wheels too
 for sibling in ${ZUUL_SIBLINGS:-}; do

docker/python-builder/scripts/install-from-bindep

@@ -32,11 +32,17 @@ for extra in $* ; do
     EXTRAS="${EXTRAS} -f /output/$extra/requirements.txt"
 done
 
-# Install the wheels.  Use --force here because sibling wheels might
-# be built with the same version number as the latest release, but we
-# really want the speculatively built wheels installed over any
-# automatic dependencies.
-pip install --force --cache-dir=/output/wheels /output/wheels/*.whl $EXTRAS
+if [ -f /output/packages.txt ] ; then
+  # If a package list was passed to assemble, install that in the final
+  # image.
+  pip install --cache-dir=/output/wheels -r /output/packages.txt $EXTRAS
+else
+  # Install the wheels.  Use --force here because sibling wheels might
+  # be built with the same version number as the latest release, but we
+  # really want the speculatively built wheels installed over any
+  # automatic dependencies.
+  pip install --force --cache-dir=/output/wheels /output/wheels/*.whl $EXTRAS
+fi
 
 # clean up after ourselves
 apt-get clean