Fix a few grammatical errors in docs

This patch fixes a few grammatical errors in documentation.

Change-Id: I5aa92537165aa452649f71e94d6d569011b78fa4
diff --git a/doc/source/configuration.rst b/doc/source/configuration.rst
index fd9ad05..18269bf 100644
--- a/doc/source/configuration.rst
+++ b/doc/source/configuration.rst
@@ -95,7 +95,7 @@
 accounts will be assigned a role on domain configured in
 ``default_credentials_domain_name``. This will make the accounts provisioned
 usable in a cloud where domain scoped tokens are required by keystone for
-admin operations. Note that the the initial pre-provision admin accounts,
+admin operations. Note that the initial pre-provision admin accounts,
 configured in tempest.conf, must have a role on the same domain as well, for
 Dynamic Credentials to work.
 
@@ -151,7 +151,7 @@
 ``admin_domain_scope`` as ``default_credentials_domain_name`` are configured
 properly in tempest.conf.
 
-Pre-Provisioned Credentials are also know as accounts.yaml or accounts file.
+Pre-Provisioned Credentials are also known as accounts.yaml or accounts file.
 
 Compute
 -------
diff --git a/doc/source/plugin.rst b/doc/source/plugin.rst
index d34023f..285ad5d 100644
--- a/doc/source/plugin.rst
+++ b/doc/source/plugin.rst
@@ -213,7 +213,7 @@
 * **client_names**: Name of the classes that implement service clients in the
   service clients module.
 
-Example usage of the the service clients in tests::
+Example usage of the service clients in tests::
 
    # my_creds is instance of tempest.lib.auth.Credentials
    # identity_uri is v2 or v3 depending on the configuration