message: rafs/api: send rafs config json rather than a file path to nydusd
  This will make our deployment more stable since maintaining configuraion files
  everywhere is very difficult and hard to verify if it's unique as nydusd starts.
diff: @@ -14,6 +14,7 @@ use std::io::Result;
  use std::os::unix::ffi::OsStrExt;
  use std::os::unix::io::FromRawFd;
  use std::path::PathBuf;
  +use std::str::FromStr;
  use std::sync::Arc;
  use std::time::Duration;
  @@ -78,6 +79,14 @@ pub struct RafsConfig {
  pub access_pattern: bool,
  }
  +impl FromStr for RafsConfig {
  + type Err = RafsError;
  +
  + fn from_str(s: &str) -> RafsResult<RafsConfig> {
  + serde_json::from_str(s).map_err(RafsError::ParseConfig)
  + }
  +}
  +
  impl RafsConfig {
  pub fn new() -> RafsConfig {
  RafsConfig {
  