(BOLT-523) Proxy r10k logs to the bolt logger

This introduces a proxy outputter for log4r that redirects all the log
messages back to the bolt logger, where they can be sorted and handled
in the standard way.

lib/bolt/cli.rb

@@ -17,6 +17,7 @@
 require 'bolt/outputter'
 require 'bolt/puppetdb'
 require 'bolt/pal'
+require 'bolt/r10k_log_proxy'
 require 'bolt/target'
 require 'bolt/version'
 
@@ -370,8 +371,8 @@ def install_puppetfile(puppetfile, modulepath)
         }
         install_action = R10K::Action::Puppetfile::Install.new(r10k_config, nil)
 
-        # Override the r10k logger with our own logger
-        install_action.instance_variable_set(:@logger, Logging.logger[install_action])
+        # Override the r10k logger with a proxy to our own logger
+        R10K::Logging.instance_variable_set(:@outputter, Bolt::R10KLogProxy.new)
 
         ok = install_action.call
         outputter.print_puppetfile_result(ok, puppetfile, moduledir)

lib/bolt/r10k_log_proxy.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+require 'log4r/outputter/outputter'
+
+module Bolt
+  class R10KLogProxy < Log4r::Outputter
+    def initialize
+      super('bolt')
+
+      @logger = Logging.logger[self]
+    end
+
+    def canonical_log(event)
+      level = to_bolt_level(event.level)
+      @logger.send(level, event.data)
+    end
+
+    # Convert an r10k log level to a bolt log level. These correspond 1-to-1
+    # except that r10k has debug, debug1, and debug2. The log event has the log
+    # level as an integer that we need to look up.
+    def to_bolt_level(level_num)
+      level_str = Log4r::LNAMES[level_num]&.downcase || 'debug'
+      if level_str =~ /debug/
+        :debug
+      else
+        level_str.to_sym
+      end
+    end
+  end
+end