get max_tasks and thread_pool_size from config by getint()

It is OK to get max_tasks and thread_pool_size by getfloat()

The max_tasks will be passed to the Queue as maxsize and the
thread_pool_size is the thread number of the task thread pool.

So int is more reasonable than float

Change-Id: I9fc719b1b4238b0df2d9c882777cb75d7a27d4df
Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>
Signed-off-by: Adam Litke <alitke@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/9035
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>