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/quickstart/quickstart.py

@@ -14,10 +14,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""This application demonstrates label detection using the Google Cloud API.
+"""This application demonstrates label detection on a demo video using
+the Google Cloud API.
 
 Usage:
     python quickstart.py
+
 """