regression in unit tests - environment outdated since 3.9.2-45. Fixes #1993

[phillxnet]

Adds previously omitted python imports and associated settings to template file test-settings.conf.in. These same changes were previously only applied to the non testing environment template file settings.conf.in.

Fixes test_btrfs* runs.

Fixes #1993

@schakrava Ready for Review.
Apologies as I recently broke (via omission) the test environment (in pr #1990 ) and this is the fix.

Proof of fix (using test_btrfs subset of unit tests):
before pr:

./bin/test --settings=test-settings -v 3 -p test_btrfs*
...
AttributeError: 'Settings' object has no attribute 'SHUTDOWN'

after pr:

./bin/test --settings=test-settings -v 3 -p test_btrfs*
test_balance_status_cancel_requested (fs.tests.test_btrfs.BTRFSTests) ... ok
test_balance_status_finished (fs.tests.test_btrfs.BTRFSTests) ... ok
test_balance_status_in_progress (fs.tests.test_btrfs.BTRFSTests) ... ok
test_balance_status_pause_requested (fs.tests.test_btrfs.BTRFSTests) ... ok
test_balance_status_paused (fs.tests.test_btrfs.BTRFSTests)
Test to see if balance_status() correctly identifies a Paused balance ... ok
test_balance_status_unknown_parsing (fs.tests.test_btrfs.BTRFSTests) ... ok
test_balance_status_unknown_unmounted (fs.tests.test_btrfs.BTRFSTests) ... ok
test_degraded_pools_found (fs.tests.test_btrfs.BTRFSTests) ... ok
test_dev_stats_zero (fs.tests.test_btrfs.BTRFSTests) ... ok
test_device_scan_all (fs.tests.test_btrfs.BTRFSTests) ... ok
test_device_scan_parameter (fs.tests.test_btrfs.BTRFSTests) ... ok
test_get_dev_io_error_stats (fs.tests.test_btrfs.BTRFSTests) ... ok
test_get_pool_raid_levels_identification (fs.tests.test_btrfs.BTRFSTests) ... ok
test_get_property_all (fs.tests.test_btrfs.BTRFSTests) ... ok
test_get_property_compression (fs.tests.test_btrfs.BTRFSTests) ... ok
test_get_property_ro (fs.tests.test_btrfs.BTRFSTests) ... ok
test_get_snap_2 (fs.tests.test_btrfs.BTRFSTests) ... ok
test_get_snap_legacy (fs.tests.test_btrfs.BTRFSTests) ... ok
test_is_subvol_exists (fs.tests.test_btrfs.BTRFSTests) ... ok
test_is_subvol_nonexistent (fs.tests.test_btrfs.BTRFSTests) ... ok
test_parse_snap_details (fs.tests.test_btrfs.BTRFSTests) ... ok
test_scrub_status_cancelled (fs.tests.test_btrfs.BTRFSTests) ... ok
test_scrub_status_conn_reset (fs.tests.test_btrfs.BTRFSTests) ... ok
test_scrub_status_finished (fs.tests.test_btrfs.BTRFSTests) ... ok
test_scrub_status_halted (fs.tests.test_btrfs.BTRFSTests) ... ok
test_scrub_status_running (fs.tests.test_btrfs.BTRFSTests) ... ok
test_share_id (fs.tests.test_btrfs.BTRFSTests) ... ok
test_shares_info_legacy_system_pool_fresh (fs.tests.test_btrfs.BTRFSTests) ... ok
test_shares_info_legacy_system_pool_used (fs.tests.test_btrfs.BTRFSTests) ... ok
test_shares_info_system_pool_post_btrfs_subvol_list_path_changes (fs.tests.test_btrfs.BTRFSTests) ... ok
test_shares_info_system_pool_used (fs.tests.test_btrfs.BTRFSTests) ... ok
test_snapshot_idmap_home_rollback (fs.tests.test_btrfs.BTRFSTests) ... ok
test_snapshot_idmap_home_rollback_snap (fs.tests.test_btrfs.BTRFSTests) ... ok
test_snapshot_idmap_mid_replication (fs.tests.test_btrfs.BTRFSTests) ... ok
test_snapshot_idmap_no_snaps (fs.tests.test_btrfs.BTRFSTests) ... ok
test_snapshot_idmap_snapper_root (fs.tests.test_btrfs.BTRFSTests) ... ok
test_volume_usage (fs.tests.test_btrfs.BTRFSTests) ... ok

----------------------------------------------------------------------
Ran 37 tests in 0.044s

OK