copy.deepcopy() fails when using a SessionOrientedStub

[alexshpilkin]

Describe the bug

Attempting to use copy.deepcopy() fails when using a pyVim.connect.VimSessionOrientedStub, while (since the fix introduced in a90023f) it works correctly for the bare pyVmomi.SoapStubAdapter.

Reproduction steps

>>> import copy, pyVim.connect, pyVmomi
>>> stub = pyVim.connect.VimSessionOrientedStub(
...     pyVim.connect.SmartStubAdapter(host='vcenter.example', disableSslCertValidation=True),
...     pyVim.connect.VimSessionOrientedStub.makeUserLoginMethod('administrator@vsphere.local', 'swordfish'))
>>> copy.deepcopy(pyVmomi.vim.ServiceInstance('ServiceInstance', stub.soapStub))
'vim.ServiceInstance:ServiceInstance'
>>> copy.deepcopy(pyVmomi.vim.ServiceInstance('ServiceInstance', stub))
[...]
TypeError: cannot pickle '_thread.lock' object

Expected behavior

copy.deepcopy() should work equally well for SoapStubAdapters and VimSessionOrientedStubs.

Additional context

Tested on 8.0.2.0.1, but I see no relevant code changes since then.