Allow tenant isolation by default

Many people running into the issue of forgetting
to allow tenant isolation when running tempest in parallel.

Since the parallel is the `default mode`, the default config
should support this use case.

Change-Id: Ia30cfbc239c8b8628ac0926424c4100d013cd620
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index bc4198f..d81d3bb 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -125,7 +125,7 @@
 # achieved configuring a list of test accounts (boolean value)
 # Deprecated group/name - [compute]/allow_tenant_isolation
 # Deprecated group/name - [orchestration]/allow_tenant_isolation
-#allow_tenant_isolation = false
+#allow_tenant_isolation = true
 
 # If set to True it enables the Accounts provider, which locks
 # credentials to allow for parallel execution with pre-provisioned