admin: Fix cd to System cell

6250598677f3a3edccabfed9a28368b6d02db764 introduced a regression by move the
xyzzy noop command to CellAdapter and thus removing it from the System cell.
As a result, cd to the System cell resulted in an error reply. UserAdminShell
however silently ignored this error and nothing bad happened.

1e706795bfe43482d949c5dc1102fb7e513227c9 ported UserAdminShell to CellStub
which rethrows exception replies. As a consequence the UserAdminShell's cell
check would now fail, claiming that the System cell doesn't exist.

The fix adds the xyzzy command to System cell. The patch also changes
UserAdminShell to only consider TimeoutCacheException (which also covers no
route to cell errors) as a non-existing cell. Other errors are logged and
otherwise ignored.

Target: trunk
Require-notes: no
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/6841/
cells: Fix message timeout

CellNucleus relies on periodic calls to executeMaintenanceTasks for message
timeouts for asynchronous tasks to work. Every dCache cell does this
automatically by inheriting from AbstractCell, but old-scholl cells in the
cells package don't. This was not a problem as long as cells only used blocking
communication, however a recent change refactored blocking communication on top
of asynchronous communication. This broke reconnect in LocationManager.

The patch addresses the problem on two fronts: It adds an explicit timeout to
the blocking get call in sendAndWait, thus ensuring a timely timeout; and it
moves the automatic calls of executeMintenanceTasks from AbstractCell to
CellNucleus.

Target: trunk
Require-notes: no
Require-book: no
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: http://rb.dcache.org/r/6843/