[tests] Fix minor test errors

- Fix command line arguments
- Adapt error messages for rust implementations

tests/thin_restore.rs

@@ -44,7 +44,7 @@ fn no_input_file() -> Result<()> {
     let mut td = TestDir::new()?;
     let md = mk_zeroed_md(&mut td)?;
     let stderr = run_fail(thin_restore!("-o", &md))?;
-    assert!(stderr.contains("No input file provided."));
+    assert!(stderr.contains(msg::MISSING_INPUT_ARG));
     Ok(())
 }
 
@@ -54,7 +54,7 @@ fn missing_input_file() -> Result<()> {
     let md = mk_zeroed_md(&mut td)?;
     let stderr = run_fail(thin_restore!("-i", "no-such-file", "-o", &md))?;
     assert!(superblock_all_zeroes(&md)?);
-    assert!(stderr.contains("Couldn't stat file"));
+    assert!(stderr.contains(msg::FILE_NOT_FOUND));
     Ok(())
 }
 
@@ -73,7 +73,7 @@ fn no_output_file() -> Result<()> {
     let mut td = TestDir::new()?;
     let xml = mk_valid_xml(&mut td)?;
     let stderr = run_fail(thin_restore!("-i", &xml))?;
-    assert!(stderr.contains("No output file provided."));
+    assert!(stderr.contains(msg::MISSING_OUTPUT_ARG));
     Ok(())
 }