Rename ATC listing script

Rename tools/atc/email-stats.py to tools/atc/email_stats.py in
preparation for making it an importable module. This is being
separated from the subsequent change to make it more reviewable.

Change-Id: I1907de0715c96f54edb44910746fbb24a5ab8665

tools/atc/README

@@ -1,9 +1,9 @@
 These are the scripts used to create the ATC lists for use in PTL
 elections and Summit invitations.
 
-0) Write a patch to email-stats.py so steps 1-2 are not necessary.
-1) Edit email-stats.py to set your gerrit username.
-2) Edit email-stats.py to set the start_date and end_date.
+0) Write a patch to email_stats.py so steps 1-2 are not necessary.
+1) Edit email_stats.py to set your gerrit username.
+2) Edit email_stats.py to set the start_date and end_date.
 3) Run the following queries on review.openstack.org:
 
   SELECT * FROM accounts

tools/atc/email-stats.sh

@@ -7,7 +7,7 @@ for project in $(
     | grep '^ *- [A-Za-z_-]\+/[A-Za-z_-]\+$' \
     | sed 's/^ *- //'
 ) ; do
-    python email-stats.py -p $project -o out/$( basename $project ).csv
+    python email_stats.py -p $project -o out/$( basename $project ).csv
 done
 
 # Confirmed list of non-code contributors