Remove procfs dependency to make agent more compatible with other operating systems

cr https://code.amazon.com/reviews/CR-3765381

Author: footpadwolf

vendor/gems/process_manager-0.0.13/lib/process_manager/master.rb

@@ -167,7 +167,7 @@ def process_matcher(pid)
         if pid == own_pid
           return false
         end
-        File.read("/proc/#{pid}/cmdline").include?("codedeploy-agent: master")
+        `ps -p #{pid} -o command`.include?("codedeploy-agent: master")
       end
 
       def handle_pid_file