Fix a misspelled addClassResourceCleanp in tempest doc

This is to fix a misspelled addClassResourceCleanp, which
should be addClassResourceCleanup, in tempest doc

Change-Id: Ie4cdc9680016feca5f75df193077b1f0edce7e4b
diff --git a/doc/source/write_tests.rst b/doc/source/write_tests.rst
index 49af95a..fff2405 100644
--- a/doc/source/write_tests.rst
+++ b/doc/source/write_tests.rst
@@ -61,7 +61,7 @@
 
 which is executed in that order. Cleanup of resources provisioned during
 the resource_setup must be scheduled right after provisioning using
-the addClassResourceCleanp helper. The resource cleanups stacked this way
+the addClassResourceCleanup helper. The resource cleanups stacked this way
 are executed in reverse order during tearDownClass, before the cleanup of
 test credentials takes place. An example of a TestCase which defines all
 of these would be::