Improve message for ProcessExitError exception

To show as much information as possible.

lib/solid_queue/processes/process_exit_error.rb

@@ -4,10 +4,13 @@ module SolidQueue
   module Processes
     class ProcessExitError < RuntimeError
       def initialize(status)
-        message = case
-        when status.exitstatus.present? then "Process pid=#{status.pid} exited with status #{status.  exitstatus}"
-        when status.signaled? then "Process pid=#{status.pid} received unhandled signal #{status. termsig}"
-        else "Process pid=#{status.pid} exited unexpectedly"
+        message = "Process pid=#{status.pid} exited unexpectedly."
+        if status.exitstatus.present?
+          message += " Exited with status #{status.exitstatus}."
+        end
+
+        if status.signaled?
+          message += " Received unhandled signal #{status.termsig}."
         end
 
         super(message)