autotest: Refactor router configuration

1) Add new HostapConfig object which abstracts and aids router
    configuration.
2) Change new WiFi tests to configure routers through a configure()
    method on the WiFiTestContextManager.  This facillitates packet
    captures since we start the captures at configuration time.  Routing
    this call through the context lets us share a common point to
    start client/server/router captures, similar to site_wifitest.

TEST=network_WiFi_SimpleConnect/control.* pass.  Manually inspected the
802.11n parameters for correctness.
BUG=chromium:231429

Change-Id: Ifa4b92ce96094451864769bb5b3df806017773a1
Reviewed-on: https://gerrit.chromium.org/gerrit/48668
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
11 files changed