BUG/MAJOR: cli: Restore non-interactive mode behavior with pipelined commands

BUG/MAJOR: cli: Restore non-interactive mode behavior with pipelined commands

The issue was decribed in commit "BUG/MEDIUM: cli: Warn if pipelined commands
are delimited by a \n". In non-interactive mode, it was possible to use a
newline character as delimiter for pipelined commands. As a consequence, it was
possible to stop commands processing on the middle.

With the above commit, a warning is emitted to notify users. With this one,
we restore the expected behavior, as documented in the management guide.
Only the first line of commands is parsed. This commit will not be
backported to avoid breaking changes on stable versions.

This commit has of course some visible effects. All script using a newline
character as delimiter to pipeline commands in non-interactive mode will
stop working. Only the first command will be evaluated, all others will be
ignored. Pipelined commands MUST now be separated by a semi-colon.

But there is a more subtle and probably more annoying change. It is no
longer possible to pipeline commands with a payload ! A command with a
payload will always be the last one evaluated because it must be finished by
a newline (eventually preceeded by a custom pattern).

It is really annoying to introduce such breaking change. But, on the long
term, it is mandatory. The 2.8 will be the last LST version supporting the
old behavior (with some warning however). This will let 4 years to users to
adapt their scripts.

No backport needed.