Add debug output to tox_install.sh

Use -x to get proper debug output of the tool.

Paul pointed out that my previous change broke neutron and
neutron-vpnaas testing together in a very specific case. Looking at this
in detail, we need some more debugging output to fix the problem. This
script is not logged right now, so, enable logging with -x and then
uplaod logs with an infra change.

Change-Id: I6546d71c51eec74c7997d0da44db79624774c073

tools/tox_install.sh

@@ -18,6 +18,7 @@ BRANCH_NAME=master
 neutron_installed=$(echo "import neutron" | python 2>/dev/null ; echo $?)
 
 set -e
+set -x
 
 install_cmd="pip install -c$1"
 shift