Previous commit 69e935e unconditionally called pw_log_set_level() after
the option parsing. If pw_init() changed the logging level based on
PIPEWIRE_DEBUG, we'd now overwrite that change.
Call pw_log_set_level() only if -v is actually given on the commandline.
This means a commandline option will override PIPEWIRE_DEBUG if set but
that is intended.
Fixes 69e935e8a4
Override the CORE_NAME using the env variable in the context instead
of pipewire.c. This avoids needing the _add_string() property method.
Remove the properties_add_string() method, there are new improved
plans for property parsing and merging: See #207
