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
3 files changed