icsf: add support for SASL authentication

ICSF tokens can be configured using certificates to authenticate using
SASL. The certificates used are the LDAP default ones. And they can be
defined per user using the file $HOME/.ldaprc. The contents of this file
should be similar to the following example:

TLS_KEY     /path/to/client.key
TLS_CERT    /path/to/client.crt
TLS_CACERT  /path/to/ca.crt

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>