Mark (non-public API's) ctor's as explicit

Mark (non-public API's) ctor's as explicit

Make C++ class constructors that can be used with only one
required argument 'explicit' to minimize wrong use of the class.

Change-Id: I12ad5b6eb1794108c6b7464a2573e84068733b03
Reviewed-by: Sergio Ahumada <sergio.ahumada@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>