l4lx: ballooning by using new parent interface

Implement a ballooning mechanism in L4Linux similar to solutions like XEN's
balloon driver. Therefore the new parent interface extensions for requesting
and yielding resources are used. L4Linux registers a yield signal context at
its parent. Whenever the parent triggers a yield, the balloon driver blows up,
which means it requests all pages available, and then frees the corresponding
backend memory.
cli_monitor: add missing assignment statement

In the constructor of the Ram class the assignment of one constructor argument
to the corresponding member variable was missing
cli_monitor: consider instance count in quota check

In the start command when checking, whether the quota is enough to create
the new instance, consider the count of instances that should be started.
cli_monitor: limit request yields to children

Don't request resource yieldings from children that are in a resource request
themselfs to lower needless system load.
cli_monitor: don't withdraw all ram quota from child

When a yield request is responded by a child, don't withdraw all ram
quota currently available from the child, but let it keep hold a bit to live.
cli_monitor: ensure blocked children are waked up

When a command was executed, it is necessary to check not only whether the
preservation limit of the ram quota is reached, but also whether new ram quota
is available (e.g.: consequence of the kill command), and children are waiting
for additional resources.
cli_monitor: make preservation limit a hard limit

When a child requests more ram resources, it gets blocked immediately when
the preservation limit is reached. Otherwise, it might happen that the
cli_monitor runs out of memory.