Make instance start/stop skippable at burnin time

Even though burnin was born just to do that test it now contains a lot more
things one might try, so it makes sense to make instance start/stop optional
too.

This creates a burnin that at the bare minimum tests instance create and
remove, if all the --no options are specified, but usually does a lot more.

Reviewed-by: iustinp

tools/burnin

@@ -125,6 +125,9 @@ class Burner(object):
     parser.add_option("--no-importexport", dest="do_importexport",
                       help="Skip instance export/import", action="store_false",
                       default=True)
+    parser.add_option("--no-startstop", dest="do_startstop",
+                      help="Skip instance stop/start", action="store_false",
+                      default=True)
     parser.add_option("-t", "--disk-template", dest="disk_template",
                       choices=("plain", "remote_raid1", "drbd"),
                       default="remote_raid1",
@@ -359,7 +362,9 @@ class Burner(object):
       if opts.do_importexport:
         self.ImportExport()
 
-      self.StopStart()
+      if opts.do_startstop:
+        self.StopStart()
+
       has_err = False
     finally:
       if has_err: