Install python2 for Ubuntu 16.04 and CentOS 7 in Vagrant

Install python2 for Ubuntu 16.04 and CentOS 7 before executing test
script.

Change-Id: I7a7906e7431a62e6d2124bd0132236e6381bcd11

Vagrantfile

@@ -7,7 +7,6 @@ Vagrant.configure(2) do |config|
   config.vm.provision "shell", inline: <<-SHELL
     sudo su -
     cd /vagrant
-    apt-get update
     ./run_tests.sh
   SHELL
 end

run_tests.sh

@@ -17,6 +17,15 @@ set -xeuo pipefail
 
 FUNCTIONAL_TEST=${FUNCTIONAL_TEST:-true}
 
+# Install python2 for Ubuntu 16.04 and CentOS 7
+if which apt-get; then
+    sudo apt-get update && sudo apt-get install -y python
+fi
+
+if which yum; then
+    sudo yum install -y python
+fi
+
 # Install pip.
 if ! which pip; then
   curl --silent --show-error --retry 5 \