MINOR: cfgparse: add support for program section

MINOR: cfgparse: add support for program section

This patch is a part of series to reintroduce the program support in the new
master-worker architecture.

Programs are launched by master, thus only the master process needs its
configuration. Therefore, program section parser should be called only in
discovery mode, when master parses its configuration.

Program section has a post section parser. It should be called only in
discovery mode as well.