A number of subprojects inherit neutron's ServicePluginBase
class [1]. This patch rehomes ServicePluginBase into
neutron-lib along with 2 other classes required for the
implementation of ServicePluginBase.
UTs and a release note are also included.
[1] http://codesearch.openstack.org/?q=ServicePluginBase
Change-Id: I2b1131ac53e9bfeb42a92f9ef134be6ff4cfe5a3