MINOR: startup: adapt list_append_word to use cfgfile

MINOR: startup: adapt list_append_word to use cfgfile

list_append_word() helper was used before only to chain configuration file names
in a list. As now we start to use cfgfile structure which represents entire file
in memory and its metadata, let's adapt this helper to use this structure and
let's rename it to list_append_cfgfile().

Adapt functions, which process configuration files and directories to use
cfgfile structure and list_append_cfgfile() instead of wordlist.