Trains are good for writing documentation :-)
Change -S semantics a bit.

If you specify no -S file, one will be made for you.

If you truly want no authentication of CLI connections, give an
empty -S argument  (-S "") and live with the warning that causes.

Use arc4random() for challenges and secrets, we want crypto strength.
Rely on the new default -S argument
OK, now I remember why we don't use arc4random().
White-space cleanup of test-cases
Use unsigned chars when creating the secret file, in order to
not annoy FlexeLint.
Change default storage to "-smalloc,100m"

Reflect this change in varnishtest, and retire the "-storage"
keyword, storage settings can now be done with -arg.
Update the security section to reflect that -S is default now.