Re-Characterize XDCR_Commit_Timeouts as Warnings in GUI Console

See https://issues.couchbase.com/browse/CBSE-1751

Customer reported a large incidence of XDCR errors as indicated in the GUI display. On further examination, the "errors" were timeouts on XDCR commits. While these timeouts should not be ignored and Support should be involved when they are issued frequently, they are nevertheless not errors and do not cause permanent loss of replicated error. If these timeouts occur infrequently they are meaningless. When a commit timeout occurs, the transaction is reapplied transparently.

Consequently, XDCR commit timeouts should not result in replication "error" messages being displayed in the GUI; they should be displayed as warnings, preferably with a qualifying message in the GUI logs indicating that this is not a critical XDCR error and that Support should be consulted for further action if they occur frequently.