Make python interpreter option for ansible validation run

When running validation from a Train Undercloud to a
non upgraded Overcloud, the python interpreter needs to
be adjust otherwise some validations will failed due to
a wrong interpreter.
https://bugzilla.redhat.com/show_bug.cgi?id=1873470

Change-Id: Ifb987f81c6236646b83d8ab02af4631368b8ef54
rhbz: #1873470

tripleoclient/v1/tripleo_validator.py

@@ -16,6 +16,7 @@
 import argparse
 import json
 import logging
+import sys
 import yaml
 
 from osc_lib import exceptions
@@ -238,6 +239,7 @@ class TripleOValidatorRun(command.Command):
                 " run invocation. For example: --limit \"compute-0,"
                 " compute-1, compute-5\".")
         )
+
         parser.add_argument('--playbook',
                             nargs="*",
                             default=None,
@@ -246,6 +248,13 @@ class TripleOValidatorRun(command.Command):
                                    "or a list of playbook.")
                             )
 
+        parser.add_argument(
+            '--python-interpreter',
+            action='store',
+            default="/usr/bin/python{}".format(sys.version_info[0]),
+            help=_("Python interpreter for Ansible execution. ")
+        )
+
         extra_vars_group = parser.add_mutually_exclusive_group(required=False)
 
         extra_vars_group.add_argument(
@@ -341,6 +350,7 @@ class TripleOValidatorRun(command.Command):
             validations_dir=constants.ANSIBLE_VALIDATION_DIR,
             validation_name=parsed_args.validation_name,
             extra_env_vars=parsed_args.extra_env_vars,
+            python_interpreter=parsed_args.python_interpreter,
             quiet=parsed_args.quiet)
 
         # Build output