The ProxyLogger must only be set after mainLog is fully initialized.
However, it's being set before the final initialization of mainlog,
causing it still refers to stale old pointer.
To fix this, introduce a new function to discard ProxyLogger explicitly,
and use this function to init logging for all interactive commands.
So these events will be recorded separately from normal runtime log,
making troubleshooting later more easily.
While at it, only update ctrld.ProxyLogger for runCmd, it's the only one
which needs to log the query when proxying requests.
Without verbose log, we use internal log writer with log level set to
debug. However, this will affect other writers, like console log, since
they are default to notice level.
By adopting FilteredLevelWriter, we can make internal log writer run in
debug level, but all others will run in default level instead.
Without reading the documentation, users may think that "ctrld start"
will just start ctrld service. However, this is not the case, and may
lead to unexpected result from user's point of view.
This commit changes "ctrld start" to just start already installed ctrld
service, so users won't lost what they did installed before. If there
are any arguments specified, performing the current behavior.
