Stop relying on the tempest sample config file

This commit stops using the sample config file as the base for tempest
configuration. The sample config isn't actually needed as a based for
configuration because all the options are commented out so from the
perspective of the config parser it's a blank file.

There are 2 reasons for making this change, first using the sample
like this creates a hard dependency on tempest having a sample config
file in tree. This is something that the project wants to change since
keeping the file in sync causes headaches because of new oslo
releases. The second aspect is that it makes the generated output
difficult to read. It includes *every* option and it's description in
the generated output which makes finding where devstack is actually
setting something more difficult to find.

Change-Id: I4064a041a965ed2419b68efc8dc31fce37b24cfd

lib/tempest

@@ -167,10 +167,10 @@ function configure_tempest {
         esac
     fi
 
-    # Create ``tempest.conf`` from ``tempest.conf.sample``
-    # Copy every time because the image UUIDS are going to change
+    # (Re)create ``tempest.conf``
+    # Create every time because the image UUIDS are going to change
     sudo install -d -o $STACK_USER $TEMPEST_CONFIG_DIR
-    install -m 644 $TEMPEST_DIR/etc/tempest.conf.sample $TEMPEST_CONFIG
+    rm -f $TEMPEST_CONFIG
 
     password=${ADMIN_PASSWORD:-secrete}