Fix post and periodic jobs

The usage of zuul-cloner in tox_install breaks post and periodic jobs.
Update the script, it does not need to handle unconstrainted installs
anymore (see tox.ini). There's no need to set ZUUL_BRANCH explicitely
- it's set via the environment and branch is passed in as well.

Note that this script is needed for the edit-constraints call, add a
comment.

Change-Id: I0077c986a17d6bb92791474e03d1e77776e9382f
Closes-Bug: #1615430

tools/tox_install.sh

@@ -15,8 +15,6 @@ CONSTRAINTS_FILE=$1
 shift
 
 install_cmd="pip install"
-if [ $CONSTRAINTS_FILE != "unconstrained" ]; then
-
 mydir=$(mktemp -dt "$CLIENT_NAME-tox_install-XXXXXXX")
 localfile=$mydir/upper-constraints.txt
 if [[ $CONSTRAINTS_FILE != http* ]]; then
@@ -29,7 +27,7 @@ if [ $CONSTRAINTS_FILE != "unconstrained" ]; then
     echo "ALREADY INSTALLED" > /tmp/tox_install.txt
     echo "Requirements already installed; using existing package"
 elif [ -x "$ZUUL_CLONER" ]; then
-        export ZUUL_BRANCH=${ZUUL_BRANCH-$BRANCH}
+    # If this is called in a periodic job, these will not be set
     echo "ZUUL CLONER" > /tmp/tox_install.txt
     pushd $mydir
     $ZUUL_CLONER --cache-dir \
@@ -48,8 +46,10 @@ if [ $CONSTRAINTS_FILE != "unconstrained" ]; then
     $install_cmd -U -e ${REQUIREMENTS_PIP_LOCATION}
 fi
 
+# This is the main purpose of the script: Allow local installation of
+# the current repo. It is listed in constraints file and thus any
+# install will be constrained and we need to unconstrain it.
 edit-constraints $localfile -- $CLIENT_NAME "-e file://$PWD#egg=$CLIENT_NAME"
-fi
 
 $install_cmd -U $*
 exit $?