Modified a function-alert test.

[Masayuki-Hirayabu]

Hello.

In Present, the function-alert test is failed when the volume to place a data directory is small, because an alert is triggered when a remaining volume of a pg_global falls below a threshold.

The places that cause the test to fail are follows.
The test overwrites a remaining volume of pg_default to make it look smaller for triger a alert.
It is set in the following places.

pg_statsinfo/test/script/function-alert.sh

Line 162 in 67e35c3

UPDATE statsrepo.tablespace SET (avail, total) = (1.9*1024^3, 10*1024^3) WHERE name = 'pg_default' AND snapid = 2;

And the log output at this time is follows.
The second line is the log that causes the test to failed.

free disk space ratio at 'pg_default' fell below threshold in snapshot 'xxx' --- 19 % (threshold = 20 %)
free disk space ratio at 'pg_global' fell below threshold in snapshot 'xxx' --- 18.8 % (threshold = 20 %)

Test results should not diffrent by environment, so I propose this solution.
It is the test overwrites a remaining volume of pg_global to make it look bigger for not triger a alert.
This is made alerted in only pg_default.

As a side note, another solution is eixsted for this problem.
It is the test overwrites a remaining volume of pg_global to make it look smaller for triger a alert.
This is made alerted in both pg_default and pg_blobal.
But, the purpose of this test is to confirm that an alert will be triggered when a remaining volume is below the threshold, so it only needs to be confirmed in one tablespace.