Description of problem:
It is not possible to create acl group and acl user with same names. Also name of user/group cannot be the same as for example resource.

Version-Release number of selected component (if applicable):
[root@rhel72-node5 ~]# rpm -q pcs
pcs-0.9.143-15.el7.x86_64

How reproducible:
Always.

Steps to Reproduce:
1. Create acl user:
[root@rhel72-node5 ~]# pcs acl user create testname
2. Try to add group with same name as user to the acl configuration:
[root@rhel72-node5 ~]# pcs acl group create testname
Error: testname already exists

Actual results:
It is not possible to create user and group with same name.

Expected results:
It should be possible to create user and group with same name.