Find the console log handler by type when changing verbosity (#899)

* Find the console log handler by type when changing verbosity

set_verbose_logging() adjusted the first handler on the "mvt" logger,
whichever handler that happened to be. Anything else attaching a
handler to that logger - an embedding application, a plugin, a test
harness - had it mistaken for the console and raised or lowered behind
its back, and the same slot can hold the file handler a command
attaches to its output folder, whose level a --verbose flag should
never decide: command.log records the whole run either way.

Walk the handlers instead and adjust only MVT's own console handler,
found by its MVTLogHandler type. Every other handler on the logger is
left alone. Behaviour is otherwise unchanged.

* Add a --verbose option to the mvt, mvt-ios and mvt-android commands

Verbosity was an option of each module-running command, so
"mvt-ios --verbose check-backup" was a usage error, a plugin command had to
define a flag of its own, and there was no way to get debug output from mvt at
all.

The option now sits on the three commands themselves and sets the level of
MVT's console handler for the run, through set_verbose_logging(), before any
command runs. Plugin commands registered on any of the three CLIs get the
option for free and need none of their own.

The per-command --verbose of the check-* commands is kept for backward
compatibility. It only ever raises the level, so the CLI's choice is never
undone by a command's default, and its help text says it is kept for
compatibility. It is to be removed in a later release.

docs/android/intrusion_logs.md

@@ -58,7 +58,7 @@ mvt-android check-intrusion-logs --output /path/to/results/ /path/to/intrusion-l
 | `-l, --list-modules` | List the available intrusion-log modules and exit. |
 | `-m, --module NAME` | Run a single module (e.g. `DnsEvent`) instead of all of them. |
 | `-t, --timezone TZ` | IANA timezone name for the device (e.g. `Europe/Paris`). When set, event timestamps are converted to the device's local time instead of UTC. |
-| `-v, --verbose` | Verbose logging. |
+| `-v, --verbose` | Verbose logging. Kept for compatibility and to be removed in a future release: pass `--verbose` to `mvt-android` itself instead. |
 
 ## Modules