Trivial fix of doc string

Doc string of BaseComputeTest::server_check_teardown was corrected

Change-Id: I3d543d7d4d5ffbedc44ef39bf46cfdfd0389b839
diff --git a/tempest/api/compute/base.py b/tempest/api/compute/base.py
index ec2192f..b3f69c1 100644
--- a/tempest/api/compute/base.py
+++ b/tempest/api/compute/base.py
@@ -147,7 +147,7 @@
            Method will delete the server when it's dirty.
            The setUp method is responsible for creating a new server.
            Exceptions raised in tearDown class are fails the test case,
-           This method supposed to use only by tierDown methods, when
+           This method supposed to use only by tearDown methods, when
            the shared server_id is stored in the server_id of the class.
         """
         if getattr(cls, 'server_id', None) is not None: