Rename zuul-launcher to zuul-executor

To avoid confusion with nodepool-launcher, we've decided to rename
zuul-launcher to zuul-executor.

Change-Id: I7d03cf0f0093400f4ba2e4beb1c92694224a3e8c
Signed-off-by: Paul Belanger <pabelanger@redhat.com>
diff --git a/doc/source/quick-start.rst b/doc/source/quick-start.rst
index 82779c6..6d16c92 100644
--- a/doc/source/quick-start.rst
+++ b/doc/source/quick-start.rst
@@ -19,7 +19,7 @@
 Zuul provides the following components:
 
     - **zuul-server**: scheduler daemon which communicates with Gerrit and
-      Gearman. Handles receiving events, launching jobs, collecting results
+      Gearman. Handles receiving events, executing jobs, collecting results
       and postingreports.
     - **zuul-merger**: speculative-merger which communicates with Gearman.
       Prepares Git repositories for jobs to test against. This additionally