Add the CommonTimeManagementService.

Add a small service to the high level core set of system services to
control the configuration of the native common time service.  This
service is responsible for controlling policy regarding when the
common time service should be allowed to run, which networks it is
allowed to run on, what priority it runs at in the master election
algorithm, and so on.

Change-Id: I1fcd834c0286aea0df9557520693a3f42de59d69
Signed-off-by: John Grossman <johngro@google.com>