Custom BufferedWriter implementation without newLine()

This BufferedWriter does not provide newLine() method and does not read the
line.separator property via AccessController when its initialized. Whithout this
expensive call, its allocation is much faster. Used in netconf message encoder
to make the netconf serialization faster.

Change-Id: I88a65c7a82ff7c44b9ad3a3adfe7d7482a5fdc70
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>