LDAP: Use randomized ccname for storing credentials
https://fedorahosted.org/sssd/ticket/2410
If two ldap_child processes attempt to prime the ccache at the same time
for the same domain, the ldap_child might fail with:
[ldap_child_get_tgt_sync] (0x0040): Failed to init ccache: Internal credentials cache error
[main] (0x0020): ldap_child_get_tgt_sync failed.
To avoid the race-condition, the ldap_child process now creates the
ccache randomized and before returning to the caller, renames the
randomized ccache to a permanent one.
Reviewed-by: Sumit Bose <sbose@redhat.com>