Description of problem:
Alerts are not raised when Cached memory is utilized.

Version-Release number of selected component (if applicable):
tendrl-ansible-1.6.3-10.el7rhgs.noarch
tendrl-api-1.6.3-8.el7rhgs.noarch
tendrl-api-httpd-1.6.3-8.el7rhgs.noarch
tendrl-commons-1.6.3-13.el7rhgs.noarch
tendrl-grafana-plugins-1.6.3-16.el7rhgs.noarch
tendrl-grafana-selinux-1.5.4-2.el7rhgs.noarch
tendrl-monitoring-integration-1.6.3-16.el7rhgs.noarch
tendrl-node-agent-1.6.3-11.el7rhgs.noarch
tendrl-notifier-1.6.3-4.el7rhgs.noarch
tendrl-selinux-1.5.4-2.el7rhgs.noarch
tendrl-ui-1.6.3-14.el7rhgs.noarch

How reproducible:
100%

Steps to Reproduce:
1. Import cluster into WA.
2. Utilize cached memory with `stress-ng` tool.
For example: stress-ng --vm 1 --vm-bytes N
where N is 90% of total memory
3. Check alerts (UI, mail, snmp)

Actual results:
No alert is generated.

Expected results:
There should be alert that memory is utilized.

Additional info:
Alerts for Used memory are generated.