Signed-off-by: TAGOMORI Satoshi <tagomoris@gmail.com>

Plugin type is a string value, so the test should exepect a string
value while the previous out_forward code pass a symbol value as a
service_discovery plugin type by one-off code.

Signed-off-by: Takuro Ashie <ashie@clear-code.com>

A test should ensure to have only one assertion because trailing
assertions aren't evalueated when an assertions is failed. It makes
debugging hard. Here is an example output of the test:

before:

  Failure: test: server is an abbreviation of static type of service_discovery(ForwardOutputTest)
  /home/aho/Projects/Fluentd/fluentd/test/plugin/test_out_forward.rb:282:in `block in <class:ForwardOutputTest>'
  <1234> expected but was
  <1235>

  diff:
  ? 1234
  ?    5

after:

  Failure: test: server is an abbreviation of static type of service_discovery(ForwardOutputTest)
  /home/aho/Projects/Fluentd/fluentd/test/plugin/test_out_forward.rb:281:in `block in <class:ForwardOutputTest>'
  <[{:host=>"127.0.0.1", :port=>1234}, {:host=>"127.0.0.1", :port=>1235}]> expected but was
  <[{:host=>"127.0.0.1", :port=>1235}, {:host=>"127.0.0.1", :port=>1234}]>

  diff:
  ? [{:host=>"127.0.0.1", :port=>1234}, {:host=>"127.0.0.1", :port=>1235}]
  ?                                 5                                  4

The later one is easy to understand that the array is inverted.

Signed-off-by: Takuro Ashie <ashie@clear-code.com>

"server" directive should have higher priority than "service" in
"service_discovery" to keep backward compatibility.

Signed-off-by: Takuro Ashie <ashie@clear-code.com>