8 unit tests do not mock out kv() leading to lock errors in parallel run tests

[Alex Kavanagh]

The 8 unit tests are:

    unit_tests.test_percona_hooks.TestUpgradeCharm.test_upgrade_charm_leader
    unit_tests.test_percona_hooks.TestClusterRelation.test_needs_to_be_mark_as_seeded
    unit_tests.test_percona_utils.UtilsTestsStatus.test_bootstrapped_not_in_sync_to_synced
    unit_tests.test_percona_utils.UtilsTestsStatus.test_not_bootstrapped
    unit_tests.test_percona_utils.UtilsTestsStatus.test_insufficient_peers
    unit_tests.test_percona_utils.UtilsTestsStatus.test_single_unit
    unit_tests.test_percona_utils.UtilsTestsStatus.test_bootstrapped_in_sync
    unit_tests.test_percona_utils.UtilsTestsStatus.test_bootstrapped_not_in_sync

This results in a race (for py37 definitely observed: https://review.opendev.org/c/openstack/charm-percona-cluster/+/761449) where a test will fail because another, parallel running unit test, is holding a lock on the underlying SQLite database). kv() should be mocked out for these tests.

[Alex Kavanagh (ajkavanagh)]

Submitted review to resolve this issue:
https://review.opendev.org/c/openstack/charm-percona-cluster/+/764384

[Alex Kavanagh (ajkavanagh)]

Fix was merged on 2020-11-27.