Modify -T option to accept a test.tag.prefix

Signed-off-by: Olaf Kirch <okir@suse.de>
test script: add a check to verify that rpcbind runs as non-root user

Signed-off-by: Olaf Kirch <okir@suse.de>
Call rpctest -T with the name of the current test case

Signed-off-by: Olaf Kirch <okir@suse.de>