ldap: change from ping to ldap attempts

ICMP ping might be disabled between the ldap server and OBS. ping
test is not very good, as it doesn't tell if LDAP is actually running
on the server.

Instead just try connecting ldap server until ldap_max_attempts is
reached.

src/api/app/models/user_ldap_strategy.rb

@@ -551,24 +551,24 @@ def self.initialize_ldap_con(user_name, password)
     return unless defined?(CONFIG['ldap_servers'])
     require 'ldap'
     ldap_servers = CONFIG['ldap_servers'].split(":")
-    ping = false
-    server = nil
     count = 0
 
     max_ldap_attempts = CONFIG.has_key?('ldap_max_attempts') ? CONFIG['ldap_max_attempts'] : 10
 
-    while !ping && count < max_ldap_attempts
+    while count < max_ldap_attempts
       count += 1
       server = ldap_servers[rand(ldap_servers.length)]
-      # Ruby only contains TCP echo ping.  Use system ping for real ICMP ping.
-      ping = system("ping", "-c", "1", server)
+      conn = try_ldap_con(server, user_name, password)
+      if !conn.nil? && conn.bound?
+          return conn
+      end
     end
 
-    if count == max_ldap_attempts
-      Rails.logger.debug("Unable to ping to any LDAP server: #{CONFIG['ldap_servers']}")
-      return
-    end
+    Rails.logger.error("Unable to bind to any LDAP server: #{CONFIG['ldap_servers']}")
+    nil
+  end
 
+  def self.try_ldap_con(server, user_name, password)
     # implicitly turn array into string
     user_name = [user_name].flatten.join('')