all: use config_parse_file function in all plugins

all: use config_parse_file function in all plugins

Replace all usages of `config_parse_file()` in plugins with the new
`ulogd_parse_configfile()` function, adding error handling where it was
missing. I used the same codestyle as the surrounding code, which varies
between plugins.

Signed-off-by: Corubba Smith <corubba@gmx.de>
Signed-off-by: Florian Westphal <fw@strlen.de>