Add ability to provide directory filter to tailDir sink in case of recursing into subdirs

Currently tailDir accepts regex parameter that is used to filter files to be tailed. In case of recursing into subdirs (FLUME-410) filter is not applied to directories. Ability to filter directories to recurse into (i.e. the ones to tail) should be provided.

Suggestions:

• add extra param for filtering dirs on regex
• filter files & dirs based on full path. E.g. user could use "subdir[12](/..log)?" to tail subdir1/.log and subdir2/*.log