Add a keep connected for test reason

This has been sorely needed for a while. Instead of filing requests
for each of your networks in a CSTest, which is fiddly at best and
sometimes almost impossible (because you can't single out the network),
you can now add this flag and be done with it.

Test: CSKeepConnectedTest
Change-Id: Ie168fe1f3a17de035fdf05e3d6580d3262a3448e