Support python 3 in kolla-ansible script

The kolla-ansible script uses a python interpreter to detect the
location of playbooks and to check that the kolla_ansible python module
is importable. This change updates the script to support a python
interpreter named python or python3.

Partially Implements: blueprint python-3

Change-Id: Id5dcc53cc5dd9780632c04b6b73c56ea5da484a2

tools/kolla-ansible

@@ -3,7 +3,10 @@
 # This script can be used to interact with kolla via ansible.
 
 function find_base_dir {
-    local real_path=$(python -c "import os;print(os.path.realpath('$0'))")
+    # $1: Python interpreter
+    local python
+    python=$1
+    local real_path=$($python -c "import os;print(os.path.realpath('$0'))")
     local dir_name="$(dirname "$real_path")"
     if [ -z "$SNAP" ]; then
         if [[ ${dir_name} == "/usr/bin" ]]; then
@@ -120,14 +123,21 @@ LONG_OPTS="help,inventory:,playbook:,skip-tags:,tags:,key:,extra:,verbose,config
 RAW_ARGS="$*"
 ARGS=$(getopt -o "${SHORT_OPTS}" -l "${LONG_OPTS}" --name "$0" -- "$@") || { usage >&2; exit 2; }
 
-if ! python -c 'import kolla_ansible' &>/dev/null; then
+# Detect which python interpreter to use.
+for python in python3 python2; do
+    if $python -c 'import kolla_ansible' &>/dev/null; then
+        PYTHON=$python
+        break
+    fi
+done
+if [[ -z $PYTHON ]]; then
     echo "ERROR: kolla_ansible has to be available in the PYTHONPATH (e.g. installed)" >&2
     exit 1
 fi
 
 eval set -- "$ARGS"
 
-find_base_dir
+find_base_dir $PYTHON
 
 INVENTORY="${BASEDIR}/ansible/inventory/all-in-one"
 PLAYBOOK="${BASEDIR}/ansible/site.yml"