Fix sql reporting start/end times

* Always send a build start event for noop jobs so that we get
  start and end times for them
* Handle builds without start or end times in the sql reporter.
  These should no longer include noop builds, but may still include
  SKIPPED builds.

Test both.

Change-Id: I73eb6bda482ebb515d231492c0769d49cf6ff28a

tests/fixtures/config/sql-driver/git/common-config/playbooks/project-test3.yaml

@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []

tests/fixtures/config/sql-driver/git/common-config/zuul.yaml

@@ -27,6 +27,9 @@
 - job:
     name: project-test2
 
+- job:
+    name: project-test3
+
 - project:
     name: org/project
     check:
@@ -36,3 +39,9 @@
             dependencies: project-merge
         - project-test2:
             dependencies: project-merge
+        # Make sure we have a "SKIPPED" result
+        - project-test3:
+            dependencies: project-test1
+        # The noop job can have timing quirks
+        - noop:
+            dependencies: project-test2