Handle multiple rpc-error in the same rpc-reply

Handle multiple rpc-error in the same rpc-reply

When multiple rpc-error is seen in a reply it was not being
caught as an error and eventually falling through the cracks
to show up as an IllegalArgumentException.

This also adds a hack/workaround for passing back all the
error messages found from each of the multiple rpc-error(s)

Also, instead of this case not being recognized as an
rpc-error, it was causing the request to wait until
the device request timeout to expire at which point it's
noted as a full RPC failure and the device is disconnected
and reconnected. Now it is recognized as an error and the
response is handled as soon as it's received and there is
no connection flap.

JIRA: NETCONF-666
Signed-off-by: Jamo Luhrsen <jluhrsen@gmail.com>
Change-Id: I71829e04d7642cfd4d1c54596f1fc7670db0d292