Reclasify 'error' messages as 'warning'

Several log messages used the 'error' level when reporting an
event that is not necessarily an error (and does not prevent sos
from continuing).

Reclassify these to the 'warning' log level instead.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
Revert change to --plugin-options parser action

Commit 6ea48cb changed the action for the -k/--plugin-option
command line argument from 'extend' to 'append'. This breaks the
handling of options that are chained with a ',':

 logs.logsize              1,logs.all_logs max size (MiB) to collect per syslog file
 logs.all_logs             off             collect all log files defined in syslog.conf

vs:

 logs.logsize              1               max size (MiB) to collect per syslog file
 logs.all_logs             on              collect all log files defined in syslog.conf

Revert to an 'append' action for this switch.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>