SES-1719 : Convert RepositoryConnectionTest to JUnit-4

Converted test to JUnit-4 so that it can use a timeout to terminate deadlocked tests.
switch surefire from forkMode to forkCount and reuseForks
SES-1719 minor rollback of earlier fix: SailConnection.begin() does need
to throw an exception if a transaction is already active on the
connection. RDFStoreTest.testMultiThreadAccess adapted to wait until a
transaction is no longer active (on the same connection) before
continuing.
Merge branch 'master' of bitbucket.org:openrdf/sesame