cashew: don't invoke D-Bus methods from within a D-Bus handler

Call D-Bus methods from main loop to avoid deadlock (see issue 8486)
Set D-Bus connection timeout to 1 sec instead of using 25 sec default
Retry failed or timed out D-Bus calls

BUG=chromium-os:8516
TEST=Manual testing on device, with flimflam running and not running.

Change-Id: I27de7b539ceacc0471e89f595154fdb04fd74e5a

Review URL: http://codereview.chromium.org/4304002