ConnectivtyService : Execute connectivityCheck in thread pool

Since this async task takes long when doing things like waiting for
network connectivity...etc, rather than holding up the single executor
of async task for the framework (app_process), run it on a thread from
the pool so other tasks can execute in parallel.

Change-Id: I7b88a4837c7e117ef47014a20c57f828b811edfb
Merge "ConnectivtyService : Execute connectivityCheck in thread pool" into du44