Provide more information in the error message during setup_ol_tls_conn()

[droideck]

Issue Description
When there's a problem with creating a new TLS context, we just fail with -1 error code.
We can improve it by providing more information that can be extracted from LDAP_OPT_DIAGNOSTIC_MESSAGE.

[droideck]

8c86704..868b6d6 389-ds-base-3.0 -> 389-ds-base-3.0
fc12ee5..7fbee99 389-ds-base-2.5 -> 389-ds-base-2.5
310c549..88cac57 389-ds-base-2.4 -> 389-ds-base-2.4
2ccff06..cbd9f29 389-ds-base-2.3 -> 389-ds-base-2.3
d9e3f3d..98f7a41 389-ds-base-2.2 -> 389-ds-base-2.2
95ee6a6..c1101aa 389-ds-base-2.1 -> 389-ds-base-2.1
5e2d637..48b974f 389-ds-base-2.0 -> 389-ds-base-2.0
661da14..571396e 389-ds-base-1.4.3 -> 389-ds-base-1.4.3