Log ident tag with --log-target stderr:ident

Use also a colon behind ident[pid] as in syslog. It are a bit many colons for debug/traces, but ...

Examples:
$ wicked --log-target stderr
::: Reading config file /etc/wicked/client.xml

$ wicked --log-target stderr:time
2013-11-07T22:02:57.442721+01:00 ::: Reading config file /etc/wicked/client.xml

$ wicked --log-target stderr:time,pid
2013-11-07T22:06:20.808775+01:00 [6742]: ::: Reading config file /etc/wicked/client.xml

$ wicked --log-target stderr:time,ident
2013-11-07T22:06:54.175985+01:00 wicked: ::: Reading config file /etc/wicked/client.xml

$ wicked --log-target stderr:time,ident,pid
2013-11-07T22:07:07.030796+01:00 wicked[6771]: ::: Reading config file /etc/wicked/client.xml