[tools] Add pike and remove mitaka from grep-all

We now have a stable/pike branch and mitaka is EOLd (though we can't yet
remove the branch because there are still projects that are using it :(

Update the grep-all script to look in releases we care about.

Change-Id: Ia3eeda9db6b5715a3bfff5fe4f0ccd3d50ebf653

tools/grep-all.sh

@@ -15,9 +15,9 @@
 # Note(tonyb): Expand HEAD into something that's hopefully more human
 #              readable
 declare -a branches=($(git describe --always) origin/master
+                     origin/stable/pike
                      origin/stable/ocata
                      origin/stable/newton
-                     origin/stable/mitaka
                     )
 
 function search() {