Fix git access denied errors when using Spring

When allowing git disk access, we call
Gitlab::GitalyClient::StorageSettings.allow_disk_access which tracks
this using a class instance variable.

When classes are unloaded by Spring, we still keep a stale
instance of Gitlab::GitalyClient::StorageSettings in Gitlab.config.
And when self.class.disk_access_denied? is called on that instance, it
was checking the class instance variable of the stale class.

We fix this by using
Gitlab::GitalyClient::StorageSettings.disk_access_denied? so that both
of them use the same class instance variable.

lib/gitlab/gitaly_client/storage_settings.rb

@@ -60,7 +60,8 @@ module Gitlab
       end
 
       def legacy_disk_path
-        if self.class.disk_access_denied?
+        # Do not use self.class due to Spring reloading issues
+        if Gitlab::GitalyClient::StorageSettings.disk_access_denied?
           raise DirectPathAccessError, "git disk access denied"
         end