Title: #233: SDAP: Fix handling of search bases
We were rewriting the sdap_domain's search bases for only the first
sdap_domain in the list, which does not work for subdomains.
Also when search bases were already initialized in sdap_domain_subdom_add,
we should only rewrite them when they were explicitly set in sssd.conf.
To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/233/head:pr233
git checkout pr233