If le-auto's installation fails, delete the venv. Fix #2332.

Leaving broken venvs around can, if it got as far as installing the venv/bin/letsencrypt script, wreck future le-auto runs, since the presence of that script means "a working LE is installed" to it. Waiting until a new version of le-auto comes out and running it would recover, but this lets re-running the same version recover as well.

letsencrypt-auto-source/letsencrypt-auto

@@ -19,7 +19,7 @@ XDG_DATA_HOME=${XDG_DATA_HOME:-~/.local/share}
 VENV_NAME="letsencrypt"
 VENV_PATH=${VENV_PATH:-"$XDG_DATA_HOME/$VENV_NAME"}
 VENV_BIN=${VENV_PATH}/bin
-LE_AUTO_VERSION="0.4.0"
+LE_AUTO_VERSION="0.5.0.dev0"
 
 # This script takes the same arguments as the main letsencrypt program, but it
 # additionally responds to --verbose (more output) and --debug (allow support
@@ -1630,6 +1630,7 @@ UNLIKELY_EOF
       # Report error. (Otherwise, be quiet.)
       echo "Had a problem while downloading and verifying Python packages:"
       echo "$PEEP_OUT"
+      rm -rf "$VENV_PATH"
       exit 1
     fi
   fi