chefctl: pass rerun count down to chef-client via env var

Summary:
In order to start properly handling chef 401s, we need to change chefctl to
pass whether chefctl is rerunning the chef client.  Then the chef handlers can
use this information to tell if a rekey event is the normal rekey (and not
report an exception to scuba), or if it has
happened multiple times (in which case an exception should still be reported).

Differential Revision: D63587866

fbshipit-source-id: 9602fbb923c8008e2617d88ecc09bd512bf341f9

chefctl/src/chefctl.rb

@@ -933,7 +933,7 @@ def do_chef_runs
       retval = 0
       num_tries = 0
       loop do
-        retval = run
+        retval = run(num_tries)
         num_tries += 1
 
         # break if we've already run chef the max number of times
@@ -1000,7 +1000,6 @@ def get_chef_env
         env['PATH'] = Chefctl::Config.path.join(File::PATH_SEPARATOR)
       end
 
-      Chefctl.logger.info("Running chef-client with the following environment variables: #{env.inspect}")
       env
     end
 
@@ -1059,7 +1058,7 @@ def output_copier_thread
     end
 
     # Perform a chef run.
-    def run
+    def run(retry_count)
       if Chefctl.lib.is_a?(Chefctl::Lib::Windows) &&
          Chefctl::Config.windows_subshell
         # TODO(yottatsa): this code is deprecated.
@@ -1082,8 +1081,14 @@ def run
             "Redirecting chef-client's output to the shell!",
           )
         end
+        chef_env = get_chef_env
+        if retry_count > 0
+          Chefctl.logger.warn("This is a rerun attempt, rerun number #{retry_count}")
+          chef_env['RETRY_COUNT'] = retry_count.to_s
+        end
+        Chefctl.logger.info("Running chef-client with the following environment variables: #{chef_env.inspect}")
         chef_client_pid = Process.spawn(
-          get_chef_env,
+          chef_env,
           *get_chef_cmd,
           # Chefctl.log_file is set at the bottom of this file by the
           # init_logger call which is always passed a file, but just