core: VmLogonCommand - missing constructor

VmLogonCommand is invoked only from client (UserPortal/REST),
hence, a missing constructor causes a RuntimeException [1]
when connecting to console. Added a new ctr without
the CommandContext parameter.

Note: InternalCommandAttribute annotation should probably be
removed as the action is performed merely from the client.

[1] "could not find matching constructor for Command class class
org.ovirt.engine.core.bll.VmLogonCommand"

Change-Id: If0c750656a01e51614553427551896cfd6b54dd5
Signed-off-by: Daniel Erez <derez@redhat.com>