SLING-3739 - No repository found at ... : ClassNotFoundException
org.apache.jackrabbit.jcr2spi.Jcr2spiRepositoryFactory

Set a well-known ClassLoader when trying to create repositories.

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1608702 13f79535-47bb-0310-9956-ffa450edef68