Extend tools/venv3.sh to support full certbot development (#4532)

tools/venv3.sh

@@ -1,8 +1,18 @@
 #!/bin/sh -xe
 # Developer Python3 virtualenv setup for Certbot
 
-export VENV_NAME="${VENV_NAME:-venv3}"
-export VENV_ARGS="--python python3"
+if command -v python3; then
+    export VENV_NAME="${VENV_NAME:-venv3}"
+    export VENV_ARGS="--python python3"
+else
+    echo "Couldn't find python3 in $PATH"
+    exit 1
+fi
 
 ./tools/_venv_common.sh \
   -e acme[dev] \
+  -e .[dev,docs] \
+  -e certbot-apache \
+  -e certbot-nginx \
+  -e letshelp-certbot \
+  -e certbot-compatibility-test