Additional logging to debug lost Wifi APs

This change adds some in-memory logging to get some information that
doesn't seem to get captured in bug reports readily. We can remove this
after we've got to the bottom of this issue.

This is the sort of log it produces in bugreport -

WifiConfigStore - Log Begin ----
16:30:06 - loadConfiguredNetwork GoogleGuest
16:30:06 - loadConfiguredNetworks loaded 1networks
16:30:06 - disableAllNetworks
16:30:06 - loadConfiguredNetwork GoogleGuest
16:30:06 - loadConfiguredNetworks loaded 1networks
WifiConfigStore - Log End ----

Bug: 10375978
Change-Id: Iaecd3b391aea3711bf376d6cb520217d3242e6f1