Retrieve build data again when the slave is known

[fungusakafungus]

When using the build wrapper functionality ("Send console log to Logstash" checkbox), the reported buildHost and buildLabel is master as the slave is not known at the time jenkins.plugins.logstash.LogstashWriter#buildData is initialized.

This PR checks if current line contains "Building remotely" and retrieves buildData again, to have it filled with slave data.

This might be not an abstracted configurable solution, but it works for us. Maybe someone has an idea how to make this generally useful. Maybe retrieve buildData every time a line is logged?

[oleg-nenashev]

It seems to be a pretty hackish approach. The best way to have it implemented is to have a reverse trigger (onActionAdded listener). But I am not sure there is such feature i n the core, need to check it

[jakub-bochenski]

Closing in favour of #38