Show primary position LSN and lag on standby leaders

[avandras]

The output looks like

+ Cluster: pgcluster (7552841415754230055) ----------+----+-------------+-----+------------+-----+
| Member   | Host       | Role           | State     | TL | Receive LSN | Lag | Replay LSN | Lag |
+----------+------------+----------------+-----------+----+-------------+-----+------------+-----+
| dc2node1 | 10.0.0.161 | Standby Leader | streaming | 57 |             |     |            |     |
+----------+------------+----------------+-----------+----+-------------+-----+------------+-----+
 Multisite dc2 is standby, replicating from dc1 (10.0.0.32,10.0.0.127:5432)
 The latest known LSN of the primary instance is 2/140A9B18, the replication lag is 0 MB

TODO: adjust unit tests

[coveralls]

Pull Request Test Coverage Report for Build 22629878616

Details

• 24 of 34 (70.59%) changed or added relevant lines in 6 files are covered.
• 18 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.2%) to 97.277%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
patroni/utils.py	4	5	80.0%
patroni/ha.py	1	3	33.33%
patroni/multisite.py	0	2	0.0%
patroni/ctl.py	9	14	64.29%

Files with Coverage Reduction	New Missed Lines	%
patroni/postgresql/config.py	1	99.88%
patroni/postgresql/init.py	6	99.28%
patroni/ha.py	11	98.17%

Totals
Change from base Build 21445912308:	-0.2%
Covered Lines:	14933
Relevant Lines:	15351

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💛 - Coveralls