Description of problem:

This bugzilla is raised in reference to https://bugzilla.redhat.com/show_bug.cgi?id=1552288

As of currently, this seems to be an issue with UI. We are collecting the AWS memory metrics since cfme version 5.9.2. However, there is an issue with memory utilization graph. 

We have reproduced this issue on our test environment and we could see the `mem_usage_absolute_average` values are captured in vmdb_production database, what we could not observe is the graph for memory utilization on the C & U utilization tab for the instances.
~~~
vmdb_production=# select timestamp, mem_usage_absolute_average from metrics where resource_name = 'rahulc-instance1';
      timestamp      | mem_usage_absolute_average 
---------------------+----------------------------
[...]
 2019-02-12 11:07:40 |           92.1889732715258
 2019-02-12 11:08:00 |           92.1889732715258
 2019-02-12 11:08:20 |           92.1889732715258
 2019-02-12 11:08:40 |           92.1889732715258
 2019-02-12 11:09:00 |           92.1889732715258
 2019-02-12 11:09:20 |           92.1889732715258
 2019-02-12 11:09:40 |           92.1889732715258
 2019-02-12 11:10:00 |           92.1889732715258
~~~


We can verify that the memory is there in rails as well:
~~~
pp Vm.find_by(:name=>"rahulc-instance1").metrics
 #<Metric:0x0000000012893228
  id: 69867,
  timestamp: Tue, 12 Feb 2019 15:50:00 UTC +00:00,
  capture_interval: 20,
  resource_type: "VmOrTemplate",
  resource_id: 96,
....
  mem_usage_absolute_average: 19.961337410001,
....
  created_on: Tue, 12 Feb 2019 15:55:26 UTC +00:00,
  derived_cpu_available: nil,
  derived_memory_available: 1024.0,
  derived_memory_used: 204.40409507841,
....
  derived_vm_used_disk_storage: 10737418240.0,
  derived_vm_allocated_disk_storage: 10737418240.0,
~~~


Version-Release number of selected component (if applicable):
5.9.4.7 

How reproducible:
Always

Actual results:
Memory Utilization Graph is not observed in C&U data

Expected results:
Memory Utilization Graph should be displayed in C&U data