Add metrics for handed bouncer

When one handed keyguard is enabled we want to track
whether the keyguard has been switched to the other
side. Also for an unlock attempt event we want to
track the side the bouncer appears on.
Example: https://paste.googleplex.com/6483938588491776

Test: m statsd_testdrive && statsd_testdrive 63 64
Bug: 194396934
Change-Id: I0f35c0013254149a41ba7cc95fab3c1e4960eb65