Fix loading current value for nexus user passwords

There's two issues solved by this commit:

- The API calls to check if the new password works always failed;
- The new password was given as the old password value when the
  call failed, making it impossible to update the password.

resources/user.rb

@@ -19,10 +19,10 @@
     # Check if we need to change the password.
     if self.class.properties[:password].is_set?(desired)
       begin
-        ::Nexus3::Api.new(api_client.endpoint, username, desired.password).request(:get, '/service/metrics/ping')
-        password 'Supercalifragilisticexpialidocious-that-does-not-exist-so-maybe-the-resource-will-need-to-converge'
-      rescue ::Nexus3::ApiError
+        ::Nexus3::Api.new(api_client.endpoint, username, desired.password).request(:get, '/service/rapture/session')
         password desired.password
+      rescue ::Nexus3::ApiError
+        password 'Supercalifragilisticexpialidocious-that-does-not-exist-so-maybe-the-resource-will-need-to-converge'
       end
     end
   rescue LoadError, ::Nexus3::ApiError => e

spec/unit/resources/user_spec.rb

@@ -43,7 +43,7 @@
                    user_response('user_with_role'),
                    user_response('user_with_role'))
 
-      stub_request(:get, 'http://localhost:8081/service/metrics/ping')
+      stub_request(:get, 'http://localhost:8081/service/rapture/session')
         .to_return(api_response(200))
     end