Fix docgen with correct path to gem's

Fixes #2251
Add creation of zipfile for the artifacts

Fixes #2221
clear the gem paths before the test rake tasks so they find previously installed plugins

Fixes #2235
Add doc generation tasks to logstash

Fixes #2256
Make the test plugins install throw bundler, so we don't have to install them every time we run the test (it makes the thing slow). Refactor also the bundler install task into a single one, making calls to it when necessary.

Fixes #2237
make sure the bundler task is just used once while bootstraping tests

Fixes #2237
make sure the fail fast test also have the bootstrap for tests done

Fixes #2237
removes the patterns from patterns dir

The core patterns are now provided by the logstash-patterns-core gem.
This empty folder can be used for custom patterns.

Fixes #2228
Refactor doc generation

- Use a generic task for installing all plugins
- Use refactored bundle install task

Fixes #2258
Add comment for locale in date filter.

For non-english environment the date filter don't parse correctly the month name. See : http://stackoverflow.com/questions/26653490/logstash-date-filter-failed-parsing

Fixes #1987
updates docs to fix #2240

Fixes #2243
Small change so apt-transport-https package is not required on Debian. Yum supports https by default.

Fixes #2243
remove integration test that has been move into its own gem

Fixes #2270
Removing the gembag and the download of the vendored files since the logic was moved into their specific gems.

Fixes #2272
Update for windows to execute rake bootstrap and bin\logstash.bat

Fixes #2085
allow implicit agent using directly a flag in cli

Fixes #1296
validate config file encoding when containing non-ascii characters

Fixes #1468
Cleaning gems dependencies from the logstash.gemspec

Fixes #2274
Generating a new lock files with Bundler 1.7.9

Fixes #2274
typo

Fixes #2274