Add run_process() to start services without screen

* USE_SCREEN defaults to True, set it to False to exec the services
  directly via bash.  SCREEN_DEV is still supported until the CI
  scripts get updated.
* The extra logging file descriptors are properly closed in the child process
  and stdout/stderr are redirected to the log files.
* The screen_rc() call is still present; this means that stack-screenrc will
  have a complete record of what was started and rejoin-stack.sh may be able
  to re-create the setup under screen.
* The python interpreter was unwilling to write to the log files without
  unbufering stdout by using PYTHONUNBUFFERED.  This feels hackish and should
  be investigated further.

Change-Id: I012ed049f2c8b185a2e6929d73edc29e167bc21f
diff --git a/stack.sh b/stack.sh
index a4106e5..3fab488 100755
--- a/stack.sh
+++ b/stack.sh
@@ -824,8 +824,17 @@
 # Configure screen
 # ----------------
 
-if [ -z "$SCREEN_HARDSTATUS" ]; then
-    SCREEN_HARDSTATUS='%{= .} %-Lw%{= .}%> %n%f %t*%{= .}%+Lw%< %-=%{g}(%{d}%H/%l%{g})'
+USE_SCREEN=$(trueorfalse True $USE_SCREEN)
+if [[ "$USE_SCREEN" == "True" ]]; then
+    # Create a new named screen to run processes in
+    screen -d -m -S $SCREEN_NAME -t shell -s /bin/bash
+    sleep 1
+
+    # Set a reasonable status bar
+    if [ -z "$SCREEN_HARDSTATUS" ]; then
+        SCREEN_HARDSTATUS='%{= .} %-Lw%{= .}%> %n%f %t*%{= .}%+Lw%< %-=%{g}(%{d}%H/%l%{g})'
+    fi
+    screen -r $SCREEN_NAME -X hardstatus alwayslastline "$SCREEN_HARDSTATUS"
 fi
 
 # Clear screen rc file
@@ -834,12 +843,6 @@
     echo -n > $SCREENRC
 fi
 
-# Create a new named screen to run processes in
-screen -d -m -S $SCREEN_NAME -t shell -s /bin/bash
-sleep 1
-
-# Set a reasonable status bar
-screen -r $SCREEN_NAME -X hardstatus alwayslastline "$SCREEN_HARDSTATUS"
 
 # Initialize the directory for service status check
 init_service_check