Description of problem:
libvirt(3.8.0-1) added new events for *PoolBuild() and *PoolDelete(), but "event-test.py" can not adapt to this now and gives traceback.

Version-Release number of selected component (if applicable):
libvirt-python-3.9.0-1.el7.x86_64
libvirt-3.9.0-14.el7_5.5.x86_64
qemu-kvm-rhev-2.10.0-21.el7_5.2.x86_64

How reproducible:
100%

Steps to Reproduce:
1.Prepare a storage pool:
# mkdir /tmp/test
# virsh pool-define test-pool.xml 
# cat test-pool.xml 
<pool type='dir'>
  <name>test-pool</name>
  <capacity unit='bytes'>160982630400</capacity>
  <allocation unit='bytes'>63092301824</allocation>
  <available unit='bytes'>97890328576</available>
  <source>
  </source>
  <target>
    <path>/tmp/test</path>
    <permissions>
      <mode>0711</mode>
      <owner>0</owner>
      <group>0</group>
      <label>system_u:object_r:virt_image_t:s0</label>
    </permissions>
  </target>
</pool>

2.Try to get pool-build event by event-test.py:
[terminal 1]# virsh pool-build test-pool
Pool test-pool built

[terminal 2]# python `locate event-test.py` --loop --all
Using uri 'qemu:///system' and event loop '--all'
Traceback (most recent call last):
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 5025, in _dispatchStoragePoolEventLifecycleCallback
    cb(self, virStoragePool(self, _obj=pool), event, detail, opaque)
  File "/usr/share/doc/libvirt-python-3.9.0/examples/event-test.py", line 613, in myStoragePoolEventLifecycleCallback
    storageEventToString(event),
  File "/usr/share/doc/libvirt-python-3.9.0/examples/event-test.py", line 609, in storageEventToString
    return storageEventStrings[event]
IndexError: tuple index out of range

3.Try to get pool-delete event by event-test.py:
[terminal 1]# virsh pool-delete test-pool
Pool test-pool deleted

[terminal 2]# python `locate event-test.py` --loop --all
Traceback (most recent call last):
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 5025, in _dispatchStoragePoolEventLifecycleCallback
    cb(self, virStoragePool(self, _obj=pool), event, detail, opaque)
  File "/usr/share/doc/libvirt-python-3.9.0/examples/event-test.py", line 613, in myStoragePoolEventLifecycleCallback
    storageEventToString(event),
  File "/usr/share/doc/libvirt-python-3.9.0/examples/event-test.py", line 609, in storageEventToString
    return storageEventStrings[event]
IndexError: tuple index out of range


Actual results:
As in step2&3, event-test.py gets traceback when pool-build or pool-delete

Expected results:
    myStoragePoolEventCallback EVENT: Storage pool test Created 0
    myStoragePoolEventCallback EVENT: Storage pool test Deleted 0

Additional info: