Description of problem:
There was a deadlocks on katello_pools when registering content hosts (45 pieces, max 5 in parallel)


Version-Release number of selected component (if applicable):
satellite-6.2.0-9.0.beta.el7sat.noarch


How reproducible:
rarely


Steps to Reproduce:
1. Have Sat with RHEL7 and Sat Tools repo synced as custom repos and RHEL7 synced as Red Hat repo (not sure if this is important)
2. Attempt to register 45 systems (max 5 in parallel) few times
   # subscription-manager register --org Default_Organization --environment Library --username admin --password changeme --force


Actual results:
rc: 70
stdout: "Registering to: capsule62.example.com:8443/rhsm"
stderr: "Task 90dbccbf-a57b-4bb5-bea7-146b7b9c1ce8: ActiveRecord::StatementInvalid: PG::Error: ERROR:  deadlock detected\nDETAIL:  Process 9939 waits for ShareLock on transaction 2727946; blocked by process 648.\nProcess 648 waits for ExclusiveLock on tuple (0,33) of relation 19660 of database 17944; blocked by process 662.\nProcess 662 waits for ShareLock on transaction 2727938; blocked by process 9939.\nHINT:  See server log for query details.\n: UPDATE \"katello_pools\" SET \"consumed\" = $1, \"updated_at\" = $2 WHERE \"katello_pools\".\"id\" = 3"


Expected results:
There should be no DB deadlock as it indicates logical issue in the application which might became more obvious/problematic in bigger scale


Additional info:
LOG:  database system is ready to accept connections
ERROR:  deadlock detected
DETAIL:  Process 9939 waits for ShareLock on transaction 2727946; blocked by process 648.
        Process 648 waits for ExclusiveLock on tuple (0,33) of relation 19660 of database 17944; blocked by process 662.
        Process 662 waits for ShareLock on transaction 2727938; blocked by process 9939.
        Process 9939: UPDATE "katello_pools" SET "consumed" = $1, "updated_at" = $2 WHERE "katello_pools"."id" = 3
        Process 648: UPDATE "katello_pools" SET "consumed" = $1, "updated_at" = $2 WHERE "katello_pools"."id" = 2
        Process 662: UPDATE "katello_pools" SET "consumed" = $1, "updated_at" = $2 WHERE "katello_pools"."id" = 2
HINT:  See server log for query details.
STATEMENT:  UPDATE "katello_pools" SET "consumed" = $1, "updated_at" = $2 WHERE "katello_pools"."id" = 3
ERROR:  deadlock detected
DETAIL:  Process 648 waits for ShareLock on transaction 2727950; blocked by process 662.
        Process 662 waits for ShareLock on transaction 2727946; blocked by process 648.
        Process 648: UPDATE "katello_pools" SET "consumed" = $1, "updated_at" = $2 WHERE "katello_pools"."id" = 2
        Process 662: UPDATE "katello_pools" SET "consumed" = $1, "updated_at" = $2 WHERE "katello_pools"."id" = 3
HINT:  See server log for query details.
STATEMENT:  UPDATE "katello_pools" SET "consumed" = $1, "updated_at" = $2 WHERE "katello_pools"."id" = 2