ci: fix flaky tests

[shreemaan-abhishek]

Description

The sls logger failure got fixed by just waiting for a while to let the workers receive update from etcd.

Whereas, no clear fix was found for lago tests failures as most failures were due to client socket timed out.
So we modify the --- exec directive of APISIX.pm to timeout one second before the exec request times out there by appropriately reporting the stdout and stderr of the exec request instead of an empty '' message.

This will help us understand the underlying reason of lago test failure and fix it in future.

Here is the verification that the test will output stdout/stderr properly when client socket times out:

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)