Sync latest config file generator from oslo-incubator

Commits included:

  e3dddd7 generator: use EXTRA_* env vars in the bash script
  e8e636c generator: add an EXTRA_LIBRARIES env variable
  6da13e8 generator: rename EXTRA_MODULES_FILE to RC_FILE
  5dce17b Use entry points to discover options in libraries
  dd9aa2b Remove unused variables
  ad17a69 Fix filter() usage due to python 3 compability
  343686b Add check_uptodate to tools/config

The library option discovery support is the main addition we're
interested in since it is required for oslo.messaging.

Change-Id: I68958ddd1c1d0c02b54002c36b97270efaaaa892
Merge "Sync latest config file generator from oslo-incubator"