[thin_check] Start refactoring metadata_checker.

features/step_definitions/thin_steps.rb

@@ -7,7 +7,20 @@ Given(/^valid metadata$/) do
   run_simple("thin_restore -i #{xml_file} -o #{dev_file}")
 end
 
-When(/^I run thin_check with (.*?)$/) do |opts|
-  run "thin_check #{opts} #{dev_file}"
+Given(/^a corrupt superblock$/) do
+  in_current_dir do
+    write_valid_xml(xml_file)
+  end
+
+  run_simple("dd if=/dev/zero of=#{dev_file} bs=4k count=1024")
+  run_simple("thin_restore -i #{xml_file} -o #{dev_file}")
+
+  in_current_dir do
+    corrupt_block(0)
+  end
+end
+
+When(/^I run thin_check with (.*?)$/) do |opts|
+  run_simple("thin_check #{opts} #{dev_file}", false)
 end