add and check indexDirs in Cookie meta

[StevenLuMT]

Descriptions of the changes in this PR:

Motivation

planning for index dir: mail talking
stage 2: add and check indexDirs in cookie meta

Changes

1. add indexDirs in cookie meta
2. check indexDirs in cookie meta
3. add a testcase for cookie

[eolivelli]

great work
some questions

1. how do we deal with rollbacks of versions ?
2. is this change backward compatible ?

[StevenLuMT]

great work some questions

1. how do we deal with rollbacks of versions ?
2. is this change backward compatible ?

@eolivelli
good question,the code is backward compatible :

1. when set the existed config ServerConfiguration#setIndexDirName, the new cookie will work
2. when not set this config, the old testcase(CookieTest) do the regression testing
3. if old bookeeper node want to upgrade this cookie, later I will add a new pr for adding a funtion in cookie_generate

[eolivelli]

there should be already a bookkeeper shell command to rewrite the cookie

[eolivelli]

LGTM

[StevenLuMT]

3. adding a funtion in cookie_generate

yes , it's cookie_generate(class name is GenerateCookieCommand.java), I will add a param for --index-dirs
another new pr @eolivelli