Update URL in testtool documentation to RFC8040.
Fix the auto-connect section to use the correct parameters,
as the 'scale-util' parameters do not work in the way
described in the documentation.
JIRA: NETCONF-947
Change-Id: I6f3a97073936fa35fe667aae6ab52d1101e0a9a3 Signed-off-by: Peter Suna <peter.suna@pantheon.tech>