Ephemeral cookie API

Add APIs for an ephemeral app to set a cookie which is a small
peice of data cached longer than the app itself. This is useful
for avoiding the user to login every time they use the ephemeral
app. The cookie is stored after an ephemeral app is uninstalled.
Normal apps or ephemeral apps upgraded to full apps can also use
these APIs with the difference that once they are uninstalled
the cookie is deleted.

The cookie size defaults to 16KB and is configurable by a global
settings which can be adjusted via gservices. Also eviction policy
is time based with a default of one month and is configurable by
a global setting which can be adjusted via gservices. If the cert
of the app cahnges (when ephemeral is installed, uninstalled and
installed again) the cooke is wiped to prevent data leaks.

This cahange also adds an API for apps to know whether they run in
an ephemeral mode since it this mode some APIs will not be available.
Another API exposed by this change is private for the system and
exposes all ephemeral apps - installed and uninstalled. Only the
system can call this API. When an ephemeral app is uninstalled the
system stores its name, icon, and permissions. When the app is
reinstalled or a full version is installed the permissions are
propagated.

Change-Id: Id4a73a7750bfbabda0bfcb9bf9018d2062e94367