BUG 1131: Removed duplicate code in builders.

Sonar Analysis showed that concrete implementations of builders have
number of similar code blocks, which deals with creating instance
of schema node.

This functionality should have only one implementiation (this
increases readibility and reduces potential places for bugs)
moved common shared functionality  to Abstract*Builder and
Abstract implementaitons of SchemaNodes.

Change-Id: Ie9d87eaa728612090f9ad3740381df1bf970d1fe
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>
Signed-off-by: Tomas Olvecky <tolvecky@cisco.com>