logcatd: trampoline persist.logd.logpersistd to logd.logpersistd

(cherry pick from 2591d483c83a09eb8689e6e7869b4ac0bfe418db)

Best practices so that device can set logd.logpersistd properties.
Values can be overriden with trampolines for persist.logd.logpersistd
values except as designed for empty content to keep out of the way.

This allows us to set logd.logpersistd* for a non-persistent collection
that does not survive a reboot, and to use persist.logd.logpersistd*
for persistent collection that does survive a reboot.

Added logd.logpersistd.enable to gate when logpersist service can be
run allowing the properties to be adjusted safely prior to this state
as is the case for device property.

NB: /init will complain when trying to trampoline an empty property,
    this is acceptable for functionality, but may be considered
    annoying from the logging perspective.

Bug: 28788401
Bug: 28813587
Bug: 28936216
Bug: 29831823
Change-Id: I97317e8eedfae4daa8e3ef39e64e7c5c23d8b573
diff --git a/logd/README.property b/logd/README.property
index 22f86b9..b2708e4 100644
--- a/logd/README.property
+++ b/logd/README.property
@@ -1,4 +1,4 @@
-The properties that logd responds to are:
+The properties that logd and friends react to are:
 
 name                       type default  description
 ro.logd.auditd             bool   true   Enable selinux audit daemon
@@ -10,8 +10,16 @@
 ro.logd.statistics         bool+ svelte+ Enable logcat -S statistics.
 ro.build.type              string        if user, logd.statistics &
                                          ro.logd.kernel default false.
+logd.logpersistd.enable    bool   auto   Safe to start logpersist daemon service
+logd.logpersistd          string persist Enable logpersist daemon, "logcatd"
+                                         turns on logcat -f in logd context.
+					 Responds to logcatd, clear and stop.
+logd.logpersistd.buffer          persist logpersistd buffers to collect
+logd.logpersistd.size            persist logpersistd size in MB
 persist.logd.logpersistd   string        Enable logpersist daemon, "logcatd"
-                                         turns on logcat -f in logd context
+                                         turns on logcat -f in logd context.
+persist.logd.logpersistd.buffer    all   logpersistd buffers to collect
+persist.logd.logpersistd.size      256   logpersistd size in MB
 persist.logd.size          number  ro    Global default size of the buffer for
                                          all log ids at initial startup, at
                                          runtime use: logcat -b all -G <value>
@@ -45,6 +53,7 @@
 persist.log.tag.<tag>      string build  default for log.tag.<tag>
 
 NB:
+- auto - managed by /init
 - bool+ - "true", "false" and comma separated list of "eng" (forced false if
   ro.build.type is "user") or "svelte" (forced false if ro.config.low_ram is
   true).