Allow incidentd to communicate with clients over pipes.

Previously we dumped the data into dropbox.  This improves a couple
things:
  - We write into dropbox via the fd, so dropbox doesn't pull from the
    incidentd directory anymore.
  - There is a new API to for priv apps to explicitly read incident
    reports. That gives incidentd finer grained control over who can
    read it (specifically, it only allows apps to access the incident
    reports they requested, or were requested for them via statsd,
    instead of getting DUMP and reading whatever they want from
    dropbox).

Test: bit incident_test:* GtsIncidentManagerTestCases:*
Bug: 123543706
Change-Id: I9a323e372c4ff95d91419a61e8a20ea5a3a860a5
diff --git a/private/incidentd.te b/private/incidentd.te
index ad6fbf3..6f10955 100644
--- a/private/incidentd.te
+++ b/private/incidentd.te
@@ -151,6 +151,7 @@
   -dumpstate
   -incident
   -incidentd
+  -priv_app
   -statsd
   -system_app
   -system_server