message: metrics: expose process start timestamp
  this gauges process_start_time_seconds following Prometheus conventions.
  Fixes
diff: @@ -32,9 +32,17 @@ mod weekly;
  use actix::Actor;
  use failure::ResultExt;
  use log::{info, trace};
  +use prometheus::IntGauge;
  use structopt::clap::{crate_name, crate_version};
  use structopt::StructOpt;
  +lazy_static::lazy_static! {
  + static ref PROCESS_START_TIME: IntGauge = register_int_gauge!(opts!(
  + "process_start_time_seconds",
  + "Start time of the process since unix epoch in seconds."
  + )).unwrap();
  +}
  +
  fn main() -> failure::Fallible<()> {
  // Parse command-line options.
  let cli_opts = cli::CliOptions::from_args();
  @@ -69,6 +77,10 @@ fn run_agent() -> failure::Fallible<()> {
  settings.identity.group
  );
  + // Expose process start timestamp.
  + let start_time = chrono::Utc::now();
  + PROCESS_START_TIME.set(start_time.timestamp());
  +
  trace!("creating actor system");
  let sys = actix::System::builder()
  .name(crate_name!())
  