CA-149811: End the connection to each slave after that host has joined the pool to prevent XenCenter showing connection lost alerts

This fixes the following issue: event.from fails with "The underlying connection was closed: A connection that was expected to be kept alive was closed by the server.".
It happens because we end the connections to the slave hosts only after all hosts have joined the pool and in the meantime event.from on a slave fails.

We fix this by ending the connection to each host immediately after the host has joined the pool.

Signed-off-by: Mihaela Stoica <mihaela.stoica@citrix.com>
CP-9928: Link licensing alerts to the Licensing page in XenCenter help

Signed-off-by: Mihaela Stoica <mihaela.stoica@citrix.com>
Merge pull request #252 from MihaelaStoica/CP-9928

CP-9928: Link licensing alerts to the Licensing page in XenCenter help
Merge pull request #251 from MihaelaStoica/CA-149811

CA-149811: End the connection to each slave after that host has joined the pool to prevent XenCenter showing connection lost alerts