core: long query response time while many simultaneously queries are running

we found the postgres running this function 'getdiskbydiskid' so many
times when the engine started which makes disaster on the sys
with 100% CPU utilization

Change-Id: I94e20d782bc4e2befaf4338f51551a2855509769
Bug-Url: https://bugzilla.redhat.com/1120088
Signed-off-by: lzelkha@redhat.com <lzelkha@redhat.com>