Add state_path config option

Some tests run and mount files to docker containers, like
scenario dynamic routing. Since we are running tempest in
container the path to child container should be present on
the host (docker starting container from the system).
Right now path is hardcoded to /tmp/ directory. This config
option is needed for that case.

Related-Prod: PRODX-31417,PRODX-46000
Change-Id: I9d9772c526a5d383ef14d0c9247b7ecdc63957fc
(cherry picked from commit 97d8477e44860545926e45f3781e131679598cd3)
diff --git a/tempest/config.py b/tempest/config.py
index 38e2a46..5dce260 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -1336,6 +1336,10 @@
                 help="The boolean flag to specify the type of environment. "
                      "Skip tests that cannot be run in production. "
                      "For example: create/delete TLDs in Designate tests."),
+    cfg.StrOpt('state_path',
+               help="The top-level directory for maintaining Tempest state. "
+                    "For example store configuration files mounted do docker "
+                    "containers."),
 ]
 
 _opts = [