calculate remaining timeout locally

instead of making assumptions on how much time to set aside for
the timeout, instead calculate the timeout for the main gate_hook
to be DEVSTACK_GATE_TIMEOUT - time elapsed when we enter the hook
- 5 minutes (to handle cleanup and upload time).

This will hopefully make accidental overage of the timeouts less
frequent occurrence.

Change-Id: I364f9c9926488699dc77dd49189d529607858316

devstack-vm-gate-wrap.sh

@@ -24,6 +24,8 @@
 
 source $WORKSPACE/devstack-gate/functions.sh
 
+start_timer
+
 PROJECTS="openstack-dev/devstack $PROJECTS"
 PROJECTS="openstack-dev/grenade $PROJECTS"
 PROJECTS="openstack-dev/pbr $PROJECTS"
@@ -242,7 +244,8 @@ export OVERRIDE_ZUUL_BRANCH=${OVERRIDE_ZUUL_BRANCH:-$ZUUL_BRANCH}
 if ! function_exists "gate_hook"; then
   # the command we use to run the gate
   function gate_hook {
-    timeout -s 9 ${DEVSTACK_GATE_TIMEOUT}m $BASE/new/devstack-gate/devstack-vm-gate.sh
+    remaining_time
+    timeout -s 9 ${REMAINING_TIME}m $BASE/new/devstack-gate/devstack-vm-gate.sh
   }
 fi
 

functions.sh

@@ -33,6 +33,18 @@ function tsfilter {
     }'
 }
 
+# create the start timer for when the job began
+function start_timer {
+    START_TIME=`date +%s`
+}
+
+function remaining_time {
+    local now=`date +%s`
+    local elapsed=$(((now - START_TIME) / 60))
+    REMAINING_TIME=$((DEVSTACK_GATE_TIMEOUT - elapsed - 5))
+    echo "Job timeout set to: $REMAINING_TIME minutes"
+}
+
 # indent the output of a command 4 spaces, useful for distinguishing
 # the output of a command from the command itself
 function indent {