Bug 1353583

Description of problem:
I was able to create one pool with 2 tasks from 2 separated sessions and browsers.
I think this should be not possible and there should be check at least in UI and/or in API.

Version-Release number of selected component (if applicable):
first monitor:
calamari-server-1.4.2-1.el7cp.x86_64
ceph-base-10.2.2-5.el7cp.x86_64
ceph-common-10.2.2-5.el7cp.x86_64
ceph-mon-10.2.2-5.el7cp.x86_64
libcephfs1-10.2.2-5.el7cp.x86_64
python-cephfs-10.2.2-5.el7cp.x86_64
rhscon-agent-0.0.13-1.el7scon.noarch

server:
ceph-ansible-1.0.5-23.el7scon.noarch
ceph-installer-1.0.12-3.el7scon.noarch
rhscon-ceph-0.0.29-1.el7scon.x86_64
rhscon-core-0.0.29-1.el7scon.x86_64
rhscon-ui-0.0.43-1.el7scon.noarch

How reproducible:
100%

Steps to Reproduce:
1. open 2 browsers and log in by different accounts
2. try to create pool with exact same name from 2 browsers in same time
3. there are 2 tasks which will success but one pool is created

Actual results:
One pool is created but 2 success tasks are created.

Expected results:
One pool will be created and there will be one task which will fail and one task which will success.
User which try to create pool with name which already exists or it is part of the running tasks for creating pool with that name will be informed that there is already pool with that name or there is no finished tasks for creating pool with that name.
This check will be part of UI and/or API.