bin/bitbake: Catch establish connection log messages

If for example you try "bitbake -m" with an invalid BBSERVER, error
messages are not displayed. This change ensures logging is in place
to catch and display such errors.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
xmlrpc: Show a better error message for connection failures

Showing a traceback when unable to connect to a bitbake server is
rather ugly. This change allows us to show a sensible error message.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bin/bitbake: No need to show tracebacks for BBHandledExceptions

For BBHandledExceptions, we've already displaced a sensible error to
the user so we don't need to do it again. Just exit with an error
value.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bin/bitbake: Clear ui-queue when starting a server

When starting a server we don't want to show the debug event queue which
is reserved for when when errors have occurred. This patch copies the UI
code to ensure the user doesn't see confusing output.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bin/bitbake: Clarify server error message

Getting an error message about --remote-server being set when really
BBSERVER was is confusing, clarify the message.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>