core: drop ConnectSingleAsyncOperation

This patch drops the ConnectSingleAsyncOperation and it's factory with
the simple use of callables.
The ConnectSingleAsyncOperation is more complicated, harder to maintain
and limited than the simple use of callables (for example, results can't
be returned from it at the moment).

There's currently no need for that infrastructure, we can execute the
needed operations from a helper or a helper method.

Change-Id: I825d80da10ef3d22de7cd68a68d854374e6c136c
Bug-Url: https://bugzilla.redhat.com/1115845
Signed-off-by: Liron Aravot <laravot@redhat.com>
core: renaming connectAllHostsToPool

connectAllHostsToPool actually connects the hosts to the related domain
storage server, therefore in this patch its name was changed to
connectHostsInUpToDomainStorageServer.

Change-Id: I15b3cfc6f4a08350b16f252df2587bd2c7737ebe
Bug-Url: https://bugzilla.redhat.com/1115845
Signed-off-by: Liron Aravot <laravot@redhat.com>