RUBY-1087 Always try to add hosts reported by the primary description

Author: estolfo

lib/mongo/cluster/topology/replica_set.rb

@@ -144,7 +144,8 @@ def servers(servers)
         #
         # @since 2.0.6
         def add_hosts?(description, servers)
-          !!(member_of_this_set?(description) && !has_primary?(servers))
+          !!(member_of_this_set?(description) &&
+              (!has_primary?(servers) || description.primary?))
         end
 
         # Whether a description can be used to remove hosts from the cluster.

lib/mongo/server/description.rb

@@ -147,7 +147,7 @@ class Description
       # Fields to exclude when comparing two descriptions.
       #
       # @since 2.0.6
-      EXCLUDE_FOR_COMPARISON = [ LOCAL_TIME, ELECTION_ID, SET_VERSION ].freeze
+      EXCLUDE_FOR_COMPARISON = [ LOCAL_TIME ].freeze
 
       # @return [ Address ] address The server's address.
       attr_reader :address
@@ -570,7 +570,6 @@ def me_mismatch?
       # @since 2.0.6
       def ==(other)
         return false if self.class != other.class
-        return true if config == other.config
         compare_config(other)
       end
       alias_method :eql?, :==

spec/mongo/cluster/topology/replica_set_spec.rb

@@ -160,6 +160,7 @@
         let(:description) do
           double('description').tap do |d|
             allow(d).to receive(:replica_set_member?).and_return(false)
+            allow(d).to receive(:primary?).and_return(false)
           end
         end
 
@@ -179,6 +180,7 @@
         double('description').tap do |d|
           allow(d).to receive(:replica_set_member?).and_return(true)
           allow(d).to receive(:replica_set_name).and_return('testing')
+          allow(d).to receive(:primary?).and_return(false)
         end
       end