Improve error log avoidance on client disconnect.
Improve error log avoidance on client disconnect.

The existing check to only log errors from websocket connections when
the error is not because the connection is being shutdown only detects
the single case where the remote client was shutdown.

This commit modifies that logic to include when the connection is being
forcibly shutdown via closing the quit channel and when it has been
shutdown from a client side close.

wallclockbuilder/btcd,dajohi/btcd,btcsuite/btcrpcclient,aakselrod/btcd,jrick/btcrpcclient,ltcsuite/ltcd,aakselrod/btcrpcclient,btcsuite/btcd,jrick/dcrd,jrick/btcd,ltcsuite/ltcd,davecgh/btcd,btcsuite/btcd,aakselrod/btcd,decred/dcrd,Roasbeef/btcd,btcsuite/btcrpcclient,dajohi/btcd,davecgh/btcd,wallclockbuilder/btcd,jrick/btcrpcclient,Roasbeef/btcd,tb00/btcd,jrick/btcd,Stash-Crypto/btcd,tb00/btcd,dajohi/btcd,aakselrod/btcrpcclient,jrick/dcrd,ppcsuite/ppcd,jrick/btcd,decred/dcrd,Stash-Crypto/btcd,ppcsuite/ppcd