Add line breaker to below dump

Summary:
* Disabled newline in dump by default between samples.
* Add command line option `br` as line breaker.

Reviewed By: dschatzberg

Differential Revision: D23878431

fbshipit-source-id: f159b0d5b4832f06c1daf58a84c77ef9fb17fcad

resctl/below/dump/src/command.rs

@@ -422,6 +422,9 @@ pub struct GeneralOpt {
     /// Days adjuster, same as -r option in replay.
     #[structopt(short = "r")]
     pub yesterdays: Option<String>,
+    /// Line break symbol between samples
+    #[structopt(long)]
+    pub br: Option<String>,
 }
 
 #[derive(Debug, StructOpt, Clone)]

resctl/below/dump/src/tmain.rs

@@ -131,6 +131,7 @@ where
 
         let json = self.get_opts().output_format == Some(OutputFormat::Json);
         let csv = self.get_opts().output_format == Some(OutputFormat::Csv);
+        let br = self.get_opts().br.clone();
 
         let mut round = 0;
 
@@ -169,8 +170,10 @@ where
                 continue;
             }
 
-            if !csv {
+            if json {
                 write!(output, "\n")?;
+            } else if br.is_some() && !csv {
+                write!(output, "{}\n", br.as_ref().unwrap())?;
             }
         }