Adds Search Path Override

If you follow the docs for developing validations, you will find
you run into an error when attempting to execute your new validation
because the code is currently hard coded to search in a path in
/usr/share where the packaging installs the validations.  For
development, you must hack the path in the script to make this work.

This patch adds a simple override where a developer can export
a path to the VALIDATIONS_BASEDIR environment variable and that will
be used as the search path for validations.  Example:

cd tripleo-validations
export VALIDATIONS_BASEDIR=$(pwd)

Depends-On: https://review.opendev.org/#/c/706196/
Change-Id: I064c11561af67d284dcf1ab024e0d600e12a8f98
(cherry picked from commit 20c791f815)

doc/source/readme.rst

@@ -378,6 +378,14 @@ When running it, it should output something like this::
     undercloud                 : ok=2    changed=0    unreachable=0    failed=0
 
 
+If you run into an issue where the validation isn't found, it may be because the
+run-validations.sh script is searching for it in the path where the packaging
+installs validations.  For development, export an environment variable named
+VALIDATIONS_BASEDIR with the value of base bath of your git repo.::
+
+    cd /path/to/git/repo
+    export VALIDATIONS_BASEDIR=$(pwd)
+
 
 Writing the full validation code is quite easy in this case because Ansible has
 done all the hard work for us already. We can use the ``ansible_memtotal_mb``

scripts/run-validations.sh

@@ -69,7 +69,7 @@ if [ ${DEBUG:-no} == "yes" ]; then
     ANSIBLE_DEBUG="-vvvv"
 fi
 
-VALIDATIONS_BASEDIR="/usr/share/openstack-tripleo-validations"
+VALIDATIONS_BASEDIR=${VALIDATIONS_BASEDIR:="/usr/share/openstack-tripleo-validations"}
 
 VAL=$(find $VALIDATIONS_BASEDIR/playbooks -type f -regex ".*playbooks\/${VALIDATION}\.y[a]?ml")
 if [[ -z ${VAL} ]]; then