logstash boot sequence cleanup & drip support fix
deprecated USE_JRUBY environment var
added USE_RUBY and USE_DRIP environment vars
centralized gem path handling in LogStash::Environment

use consistent discovery strategy
Add tests to cover codec autoswitch for stdin + tcp inputs

json->json_lines & plain->line

Tests for #1392
Closes #1394
inputs/base: Copy the codec's charset when switching.

Includes tests