phosphor-ldap-conf: handle "InterfaceAdded" signal on the ldap cert object

When LDAP client certificate is uploaded through install method on the
cert object, Object would emit the signal "InterfaceAdded".
Upon receiving the signal, Config file would be updated with
below given info if secure ldap is enabled:
     tls_cert <path client certificate file>
     tls_key  <path to client certificate file>

Tested By: Unit Tested

Signed-off-by: Ratan Gupta <ratagupt@linux.vnet.ibm.com>
Change-Id: I54b3e116af1b8a9057d91797d4074d39efc65bb0
diff --git a/configure.ac b/configure.ac
index 72acd4a..baa84a4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -71,6 +71,10 @@
 AS_IF([test "x$TLS_CACERT_FILE" == "x"], [TLS_CACERT_FILE="/etc/ssl/certs/Root-CA.pem"])
 AC_DEFINE_UNQUOTED([TLS_CACERT_FILE], ["$TLS_CACERT_FILE"], [Path of LDAP server's CA certificate])
 
+AC_ARG_VAR(TLS_CERT_FILE, [Path of LDAP's client certificate])
+AS_IF([test "x$TLS_CERT_FILE" == "x"], [TLS_CERT_FILE="/etc/nslcd/certs/cert.pem"])
+AC_DEFINE_UNQUOTED([TLS_CERT_FILE], ["$TLS_CERT_FILE"], [Path of LDAP's client certificate])
+
 AC_ARG_VAR(LDAP_CONFIG_ROOT, [LDAP configuration root])
 AS_IF([test "x$LDAP_CONFIG_ROOT" == "x"], [LDAP_CONFIG_ROOT="/xyz/openbmc_project/user/ldap"])
 AC_DEFINE_UNQUOTED([LDAP_CONFIG_ROOT], ["$LDAP_CONFIG_ROOT"], [LDAP configuration root])