[FileCache#find] N to 1 calls for regex matching

Signed-off-by: David Crosby <dcrosby@fb.com>

lib/chef/file_cache.rb

@@ -159,9 +159,15 @@ def list
       # [String] - An array of file cache keys matching the glob
       def find(glob_pattern)
         keys = []
-        Dir[File.join(Chef::Util::PathHelper.escape_glob_dir(file_cache_path), glob_pattern)].each do |f|
+        file_cache_dir = Chef::Util::PathHelper.escape_glob_dir(file_cache_path)
+        first_filename = Dir[file_cache_dir].first
+        return keys unless first_filename
+
+        path_to_remove = first_filename + File::Separator
+        Dir[File.join(file_cache_dir, glob_pattern)].each do |f|
           if File.file?(f)
-            keys << f[/^#{Regexp.escape(Dir[Chef::Util::PathHelper.escape_glob_dir(file_cache_path)].first) + File::Separator}(.+)/, 1]
+            f.delete_prefix!(path_to_remove)
+            keys << f
           end
         end
         keys