shill: log metrics for connection diagnostics issue

Log UMA metrics for the connectivity issue found whenever
ConnectionDiagnostics completes its diagnostics.

Also: add periods at the end of connection diagnostics
issue strings that were not already period-terminated.

BUG=chromium:216691
TEST=Compile shill and run unit tests.

Change-Id: I353fdb6b7d174ef6a3907de43c7299f00b6c5a98
Reviewed-on: https://chromium-review.googlesource.com/293803
Reviewed-by: Samuel Tan <samueltan@chromium.org>
Commit-Queue: Samuel Tan <samueltan@chromium.org>
Tested-by: Samuel Tan <samueltan@chromium.org>
8 files changed