Fix spare_pool_enabled option type

spare_pool_enable option should be a boolean value, as used in
SparePoolTest.skip_checks method.

Change-Id: I6fd3c95aa6e80c35e4edb66eb80f2d90eaf6c747
diff --git a/octavia_tempest_plugin/config.py b/octavia_tempest_plugin/config.py
index 7c4ed2f..bd9c8fb 100644
--- a/octavia_tempest_plugin/config.py
+++ b/octavia_tempest_plugin/config.py
@@ -209,10 +209,10 @@
                default="TCP",
                help="The type of L4 Protocol which is supported with the "
                     "provider driver."),
-    cfg.StrOpt('spare_pool_enabled',
-               default=False,
-               help="Wether spare pool is available with amphora provider "
-                    "driver or not."),
+    cfg.BoolOpt('spare_pool_enabled',
+                default=False,
+                help="Wether spare pool is available with amphora provider "
+                "driver or not."),
     cfg.BoolOpt('session_persistence_enabled',
                 default=True,
                 help="Whether session persistence is supported with the "