Do some more package installation in the ci image

.circleci/Dockerfile.debian-9

@@ -1,3 +1,13 @@
 FROM debian:9
 
-RUN apt-get --quiet update && apt-get --quiet --yes install git
+RUN apt-get --quiet update &&
+    apt-get --quiet --yes install git &&
+    apt-get --quiet --yes install \
+        sudo \
+    	build-essential \
+	python2.7 \
+    	python2.7-dev \
+    	libffi-dev \
+    	libssl-dev \
+    	libyaml-dev \
+    	virtualenv

.circleci/bootstrap-test-environment.sh

@@ -15,13 +15,3 @@ mv "${PROJECT}" /tmp/project
 
 # Python build/install toolchain wants to write to the source checkout, too.
 chown --recursive nobody:nogroup /tmp/project
-
-apt-get --quiet --yes install \
-    sudo \
-    build-essential \
-    python2.7 \
-    python2.7-dev \
-    libffi-dev \
-    libssl-dev \
-    libyaml-dev \
-    ${EXTRA_PACKAGES}

.circleci/config.yml

@@ -67,8 +67,6 @@ jobs:
       # Tell the C runtime things about character encoding (mainly to do with
       # filenames and argv).
       LANG: "en_US.UTF-8"
-      # The package name for this software varies somewhat across distros.
-      EXTRA_PACKAGES: "virtualenv"
       # Select a tox environment to run for this job.
       TAHOE_LAFS_TOX_ENVIRONMENT: "coverage"
       # Additional arguments to pass to tox.
@@ -86,7 +84,7 @@ jobs:
       - run: &BOOTSTRAP_TEST_ENVIRONMENT
           name: "Bootstrap test environment"
           command: |
-            ~/project/.circleci/bootstrap-test-environment.sh ~/project "${EXTRA_PACKAGES}"
+            ~/project/.circleci/bootstrap-test-environment.sh ~/project
 
       - restore_cache: &RESTORE_HTTP_CACHE
           name: "Restoring pip HTTP cache"