better exception handling upon invalid temp log file name

[colinsurprenant]

Per #41 if an invalid temp file name is created using, for example, an invalid pattern in log_file_prefix then the resulting exception is very hard to decrypt.

    #<Errno::ENOENT: No such file or directory - 
    /tmp/logstash-gcs-504f0f1052346b639f01477069a72f1f76be227ff8e41870e5f7859b5be1/logs/%{+YYYY/MM/dd}_logstasher-785c699966-sg4c9_2019-08-05T19:00.part001.log.gz>, 
  :backtrace=>[
    "org/jruby/RubyIO.java:1236:in `sysopen'", 
    "org/jruby/RubyFile.java:367:in `initialize'", 
    "org/jruby/RubyIO.java:876:in `new'", 
    "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-google_cloud_storage-4.0.1-java/lib/logstash/outputs/gcs/temp_log_file.rb:29:in `initialize'", 
    "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-google_cloud_storage-4.0.1-java/lib/logstash/outputs/gcs/temp_log_file.rb:14:in `create'", 
    "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-google_cloud_storage-4.0.1-java/lib/logstash/outputs/gcs/log_rotate.rb:51:in `block in rotate_log!'", 
    "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/atomic/reentrant_read_write_lock.rb:147:in `with_write_lock'", 
    "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-google_cloud_storage-4.0.1-java/lib/logstash/outputs/gcs/log_rotate.rb:42:in `rotate_log!'", 
    "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-google_cloud_storage-4.0.1-java/lib/logstash/outputs/gcs/log_rotate.rb:19:in `initialize'", 
    "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-google_cloud_storage-4.0.1-java/lib/logstash/outputs/google_cloud_storage.rb:266:in `initialize_log_rotater'", 
    "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-google_cloud_storage-4.0.1-java/lib/logstash/outputs/google_cloud_storage.rb:164:in `register'", 
    "org/logstash/config/ir/compiler/OutputStrategyExt.java:106:in `register'", 
    "org/logstash/config/ir/compiler/AbstractOutputDelegatorExt.java:48:in `register'", 
    "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:192:in `block in register_plugins'", 
    "org/jruby/RubyArray.java:1792:in `each'", 
    "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:191:in `register_plugins'", 
    "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:462:in `maybe_setup_out_plugins'", 
    "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:204:in `start_workers'", 
    "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:146:in `run'", 
    "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:105:in `block in start'"

We should improve the error reporting for this.