Rename screen logfiles

This renames the log files in logs/screen that contain timestamps to put
the timestamp after '.log' and '.log.summary' in the names.  This will
simplify devstack-gate's search for log files to copy to '*.log'.

dstat.txt is also renamed to dstat.log

Make LOGDIR and LOGFILE local

bp:devstack-logging-and-service-names
Change-Id: I02aba9ca82c117a1186dafc1d3c07aa04ecd1dde
diff --git a/lib/dstat b/lib/dstat
index 73ca279..a17125f 100644
--- a/lib/dstat
+++ b/lib/dstat
@@ -20,7 +20,7 @@
 # Defaults
 # --------
 # for DSTAT logging
-DSTAT_FILE=${DSTAT_FILE:-"dstat.txt"}
+DSTAT_FILE=${DSTAT_FILE:-"dstat.log"}
 
 
 # start_dstat() - Start running processes, including screen