[DOC] remove duplex comment
[TEST] for scenarios in testplans
[FEAT] scenarios in testplans

Scenarios are the way to have testruns that depend on each other
(interdependend testruns), e.g. client-server tests. Yet, Tapper::Cmd
support for scenarios was quite weak. the actual work was still done in
the CLI and not moved into Cmd. This did not allow handling scenarios
other than directly from the CLI.

Now we want to have scenarios in testplans to create testplans with
client-server tests. For this I moved the scenario work into Tapper::Cmd
and called these functions for the testplan handler. This way testplans
now recognise not only multitest but also scenario and thus interdep
testruns.
[FIX] TODO help string (one less)
[FIX] requested_* is no longer required

When creating a testrun with Cmd::Testrun->create() you can give
requested host or features. If you provided none of this, no testrun was
created. Obviously, in this case we want exactly one testrun on the
first available host.
[TEST] 'single' scenarios
[FEAT] new scenario type multitest

To describe a whole testrun in a file, you had to use either testplans
or interdep scenarios with just one element. Both bring additional
features that may be unwanted and don't work nicely with autorerun.

Now you can describe testruns as multitest scenarios. This mirrors the
multitest behaviour of testplans without all the testplan extensions.
[FIX] prevent requesting inexistent hosts

When a requested host does not exists, we now die().
[TEST] make sure requested hosts exist

Since requesting inexisting hosts is now a mistake, we need to make sure
that our test database contains the hosts we want to request.
Scenario->add now expects an array ref

add expects an array ref instead of a scalar. This means that you can
give multiple scenarios at once. Thus, now you can have multiple
scenarios in one file, separated by "---\n", just like other files
(e.g. macroprecondition files) already permit.
[TEST] add requested hosts to test database

requested hosts need to exist now
backwards compatibility for requested hosts in interdep

Interdep scenarios used a key "requested_hosts" which did exactly the
same as the "requested_hosts_any" we have today. It contains a list of
hosts any requests that the testrun is placed on any one of these
hosts. To make sure these old scenario descriptions still work, this
patch rewrites "requested_hosts" to "requested_hosts_any".
Merge git://github.com/tapper/Tapper-Cmd