NO-JIRA: Minor rationalization of log statement priorities.

Demote "backup of queue x connected to y" from info to debug.
Tighten up redundant 'notice' messages around promotion of primary.
Promote 'DTX not implemented' to warning
Misc. other minor adjustments.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1561833 13f79535-47bb-0310-9956-ffa450edef68