Reduce alerting noise for system disk issues

Change-Id: I4fb69e8defa44a9d92a9fb7c23a6280fffc1a3e9

linux/meta/prometheus.yml

@@ -14,6 +14,7 @@ server:
     SystemDiskSpaceTooLow:
       if: 'predict_linear(disk_free[1h], 8*3600) < 0'
       {% raw %}
+      for: 5m
       labels:
         severity: warning
         service: system
@@ -34,6 +35,7 @@ server:
     SystemDiskInodesTooLow:
       if: 'predict_linear(disk_inodes_free[1h], 8*3600) < 0'
       {% raw %}
+      for: 5m
       labels:
         severity: warning
         service: system