Add $TOP_DIR to the path when calling tools' scripts

The missing reference to $TOP_DIR prevent us to run stack.sh from a different
directory.

Change-Id: Ie15b89734264789bef9a8efcfdbbf2cdb89c936e
diff --git a/stack.sh b/stack.sh
index e73b16a..6452563 100755
--- a/stack.sh
+++ b/stack.sh
@@ -548,14 +548,14 @@
     exec 3>&1
     if [[ "$VERBOSE" == "True" ]]; then
         # Set fd 1 and 2 to write the log file
-        exec 1> >( ./tools/outfilter.py -v -o "${LOGFILE}" ) 2>&1
+        exec 1> >( $TOP_DIR/tools/outfilter.py -v -o "${LOGFILE}" ) 2>&1
         # Set fd 6 to summary log file
-        exec 6> >( ./tools/outfilter.py -o "${SUMFILE}" )
+        exec 6> >( $TOP_DIR/tools/outfilter.py -o "${SUMFILE}" )
     else
         # Set fd 1 and 2 to primary logfile
-        exec 1> >( ./tools/outfilter.py -o "${LOGFILE}" ) 2>&1
+        exec 1> >( $TOP_DIR/tools/outfilter.py -o "${LOGFILE}" ) 2>&1
         # Set fd 6 to summary logfile and stdout
-        exec 6> >( ./tools/outfilter.py -v -o "${SUMFILE}" >&3 )
+        exec 6> >( $TOP_DIR/tools/outfilter.py -v -o "${SUMFILE}" >&3 )
     fi
 
     echo_summary "stack.sh log $LOGFILE"
@@ -572,7 +572,7 @@
         exec 1>/dev/null 2>&1
     fi
     # Always send summary fd to original stdout
-    exec 6> >( ./tools/outfilter.py -v >&3 )
+    exec 6> >( $TOP_DIR/tools/outfilter.py -v >&3 )
 fi
 
 # Set up logging of screen windows