Acquire fails with "ToozError: Not found"
Acquire fails with "ToozError: Not found"

For Etcd3Lock, blocking call to acquire an already acquired lock fails
when the thread/process, that acquired the lock takes more than the
timeout specified for the lock.

Scenario
========
1. First thread acquires a lock "Lock1"
2. Second thread tries to acquire "Lock1" with blocking=True
3. First thread releases lock after few minutes
4. Second thread tries to acquire it and fails with exception:
ToozError: Not found

Cause
=====
Lease gets created when the lock is created and the default timeout is
30 secs. Since the first thread takes more than 30 seconds to complete,
the lease for the second thread gets expired leading to "Not found"
message.

Resolution
==========
Create lease within Etcd3Lock.acquire() rather than
Etcd3Lock.__init__() of Etcd3Lock

Change-Id: Ief75675ebde2d824a25aec6210e2a868cf3dbbe7
Closes-Bug: #1708836

openstack/tooz,openstack/tooz