Title: #342: SELINUX: Use getseuserbyname to get IPA seuser
I tested this by logging into my IPA client with an IPA user and AD trust user after
deleting any existing SELinux login mapping:
`# semanage login -d testuser1`
Then checking `/var/log/sssd/selinux_child.log` to verify there are no issues. I am not
sure how to try testing this patch more than this.
See the full comment at https://github.com/SSSD/sssd/pull/342#issuecomment-319146122