logd: initial checkin.

* Create a new userspace log daemon for handling logging messages.

Original-Change-Id: I75267df16359684490121e6c31cca48614d79856
Signed-off-by: Nick Kralevich <nnk@google.com>

* Merge conflicts
* rename new syslog daemon to logd to prevent confusion with bionic syslog
* replace racy getGroups call with KISS call to client->getGid()
* Timestamps are filed at logging source
* insert entries into list in timestamp order
* Added LogTimeEntry tail filtration handling
* Added region locking around LogWriter list
* separate threads for each writer
* /dev/socket/logd* permissions

Signed-off-by: Mark Salyzyn <salyzyn@google.com>

Change-Id: Ice88b1412d8f9daa7f9119b2b5aaf684a5e28098