(PUP-7520) Update Puppet profiling timers to use monotonic clock

This commit updates Puppet::Util::Profiler::WallClock and
Puppet::Util::Profiler::Aggregate to use
Process.clock_gettime(Process::CLOCK_MONOTONIC) instead of Time.now. Time.now
returns a value from the OS REALTIME clock which can be affected by events
like NTP updates. Process.clock_gettime(Process::CLOCK_MONOTONIC) uses a
monotonic clock which isn't affected by things like NTP updates.

lib/puppet/util/profiler/aggregate.rb

@@ -72,11 +72,11 @@ def add_time(time)
 
   class Timer
     def initialize
-      @start = Time.now
+      @start = Process.clock_gettime(Process::CLOCK_MONOTONIC, :float_second)
     end
 
     def stop
-      Time.now - @start
+      Process.clock_gettime(Process::CLOCK_MONOTONIC, :float_second) - @start
     end
   end
 end

lib/puppet/util/profiler/wall_clock.rb

@@ -21,11 +21,11 @@ class Timer
     FOUR_DECIMAL_DIGITS = '%0.4f'
 
     def initialize
-      @start = Time.now
+      @start = Process.clock_gettime(Process::CLOCK_MONOTONIC, :float_second)
     end
 
     def stop
-      @time = Time.now - @start
+      @time = Process.clock_gettime(Process::CLOCK_MONOTONIC, :float_second) - @start
       @time
     end