logd: logpersistd

- Enable logpersistd to write to /data/misc/logd
- Enable logpersistd to read from pstore to help complete any content
  lost by reboot disruption
- Enable shell readonly ability logpersistd files in /data/misc/logd
- Enable logcat -f when placed into logd context to act as a
  logpersistd (nee logcatd) agent, restrict access to run only in
  userdebug or eng

Bug: 19608716
Change-Id: I3209582bc796a1093c325c90068a48bf268e5ab5