Alter Android's connection pool behavior on network config changes

Rather than clearing out and closing the shared connection pool
each time the network changes with evictAll() this ensures that
later Http(s)URLConnections will reference a new ConnectionPool
instance.

This is an improvement over the current implementation:
1) It is obviously non-blocking.
2) It ensures that connections for the old network config
and are currently in use are not put back into the shared
pool.

Bug: 17314604
(cherry-picked from commit 8bced3e769d315a0a81b89de7a5282f1a85acbf7)

Change-Id: I4b2295ebceca93d55c994857de8554e9bb48b4c5
Merge "Alter Android's connection pool behavior on network config changes"