Tweak doc/help strings for sample tools [(#1160)](GoogleCloudPlatform…

…/python-docs-samples#1160)

* Corrected copy-paste on doc string

* Updated doc/help string to be more specific to labels tool

* Made shotchange doc/help string more specific

* Tweaked doc/help string to indicate no arg expected

* Adjusted import order to satisfy flake8

* Wrapped doc string to 79 chars to flake8 correctly

* Adjusted import order to pass flake8 test

samples/labels/labels.py

@@ -14,8 +14,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""This application demonstrates how to perform basic operations with the
-Google Cloud Video Intelligence API.
+"""This application demonstrates how to detect labels from a video
+based on the image content with the Google Cloud Video Intelligence
+API.
 
 For more information, check out the documentation at
 https://cloud.google.com/videointelligence/docs.