Update Context Switch Check to use Prometheus as Datasource

The previous method of using data returned by node_exporter was invalid, as it returns a total since boot.

The new method queries Prometheus to get a rate change of the same metric:

```shell
HW_CONTEXT_SWITCH_RATE=$(curl -fs --data-urlencode "query=irate(node_context_switches_total{job=\"compute-node\",name=\"$NODENAME\"}[$HW_CONTEXT_SWITCH_INTERVAL])" http://nagios.rc.uab.edu:9090/api/v1/query | jq -r '.data.result[] | .value[1]')
```

nhc.conf

@@ -212,3 +212,5 @@
 # nVidia HealthMon GPU health checks (requires Tesla Development Kit)
 #   * || check_nv_healthmon
 
+# Check for high rate of context switching
+   * || uabrc_check_hw_context_switch_rate 300000 30m

uabrc_hw.nhc

@@ -6,24 +6,30 @@
 # Copyright and/or license information if different from upstream
 #
 
-declare HW_CONTEXT_SWITCHES=0
+declare HW_CONTEXT_SWITCH_RATE=0
 
 # Gather the metrics
 function uabrc_hw_gather_data() {
-    HW_CONTEXT_SWITCHES=$(curl --silent http://localhost:9100/metrics | grep ^node_context_switches_total | awk '{print $2}' | awk '{printf("%d\n", $1*1e$2)}')
+    # HW_CONTEXT_SWITCH_RATE=$(curl --silent http://localhost:9100/metrics | grep ^node_context_switches_total | awk '{print $2}' | awk '{printf("%d\n", $1*1e$2)}')
+    HW_CONTEXT_SWITCH_RATE=$(curl -fs --data-urlencode 'query=snode_context_switches_total{job="compute-node",name="c0159"}(30m)' https://nagios.rc.uab.edu:9090/api/v1/query | jq -r '.data.result[] | [.metric.container_name, .metric.namespace, .value[1] ] | @csv')
 }
+curl -fs --data-urlencode 'query=snode_context_switches_total{job="compute-node",name="c0159"}(30m)' https://nagios.rc.uab.edu:9090/api/v1/query | jq -r '.data.result[] | [.metric.container_name, .metric.namespace, .value[1] ] | @csv'
 
 # Check that total context switches are less than max context switches ($1)
 # The total context switches is collected from Prometheus Node Exporter
-function uabrc_check_hw_context_switches() {
-    local CONTEXT_SWITCH_MAX="$1"
+function uabrc_check_HW_CONTEXT_SWITCH_RATE() {
+    local CONTEXT_SWITCH_RATE_MAX="$1"
 
-    if [[ $HW_CONTEXT_SWITCHES -eq 0 ]]; then
+    if [[ $HW_CONTEXT_SWITCH_RATE -eq 0 ]]; then
         uabrc_hw_gather_data
     fi
 
-    if [[ $((HW_CONTEXT_SWITCHES)) -gt $CONTEXT_SWITCH_MAX ]]; then
-        die 1 "$FUNCNAME:  Total Context Switches ($HW_CONTEXT_SWITCHES) greater than maximum allowed ($CONTEXT_SWITCH_MAX)."
+    if [[ $((HW_CONTEXT_SWITCH_RATE)) -gt $CONTEXT_SWITCH_RATE_MAX ]]; then
+        die 1 "$FUNCNAME:  Total Context Switches ($HW_CONTEXT_SWITCH_RATE) greater than maximum allowed ($CONTEXT_SWITCH_RATE_MAX)."
         return 1
     fi
+    echo "HW_CONTEXT_SWITCH_RATE: $HW_CONTEXT_SWITCH_RATE"
+    echo "CONTEXT_SWITCH_RATE_MAX: $CONTEXT_SWITCH_RATE_MAX"
 }
+
+uabrc_check_HW_CONTEXT_SWITCH_RATE $1
\ No newline at end of file