index_template: Handle error object entirely on index creation failure
index_template: Handle error object entirely on index creation failure

ref: https://github.com/fluent/fluentd/blob/master/lib/fluent/log.rb#L369
ref: https://github.com/fluent/fluentd/blob/adca0296bfcbb8696afa949a55e82807dd69c155/lib/fluent/log.rb#L511

Signed-off-by: Hiroshi Hatake <54b742842f0d940c9715551f77be1b560ea6cc67@gmail.com>

uken/fluent-plugin-elasticsearch