Disabled Http2_PingKeepAlive

[ManickaP]

The high numbers of failures seem to be temporary in the end. My assumption about product code change was probably false.
We might hold this PR back for a few more days to confirm this.

Numbers per day (kusto):

Disabled test tracked in #41929

Queued	Count
2020-09-26	1
2020-09-27	2
2020-09-28	2
2020-09-29	7
2020-09-30	2
2020-10-01	1
2020-10-02	4
2020-10-03	4
2020-10-04	3
2020-10-05	8
2020-10-06	1
2020-10-07	5
2020-10-08	6
2020-10-09	2
2020-10-10	2
2020-10-11	2
2020-10-13	4
2020-10-14	6
2020-10-15	4
2020-10-16	3
2020-10-17	2
2020-10-18	2
2020-10-19	3
2020-10-20	4
2020-10-21	3
2020-10-22	1
2020-10-23	2
2020-10-26	2
2020-10-30	1
2020-10-31	4
2020-11-02	1
2020-11-04	12
2020-11-05	30
2020-11-06	15
2020-11-07	22
2020-11-08	11
2020-11-09	12
2020-11-10	23
2020-11-11	15
2020-11-12	29
2020-11-13	30
2020-11-14	16
2020-11-16	17
2020-11-17	11
2020-11-18	29
2020-11-19	37
2020-11-20	16
2020-11-21	7
2020-11-25	1

[ghost]

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Issue Details

---

The high numbers of failures seem to be temporary in the end. My assumption about product code change was probably false.
We might hold this PR back for a few more days to confirm this.

Numbers per day (kusto):

Queued	Count
2020-09-26	1
2020-09-27	2
2020-09-28	2
2020-09-29	7
2020-09-30	2
2020-10-01	1
2020-10-02	4
2020-10-03	4
2020-10-04	3
2020-10-05	8
2020-10-06	1
2020-10-07	5
2020-10-08	6
2020-10-09	2
2020-10-10	2
2020-10-11	2
2020-10-13	4
2020-10-14	6
2020-10-15	4
2020-10-16	3
2020-10-17	2
2020-10-18	2
2020-10-19	3
2020-10-20	4
2020-10-21	3
2020-10-22	1
2020-10-23	2
2020-10-26	2
2020-10-30	1
2020-10-31	4
2020-11-02	1
2020-11-04	12
2020-11-05	30
2020-11-06	15
2020-11-07	22
2020-11-08	11
2020-11-09	12
2020-11-10	23
2020-11-11	15
2020-11-12	29
2020-11-13	30
2020-11-14	16
2020-11-16	17
2020-11-17	11
2020-11-18	29
2020-11-19	37
2020-11-20	16
2020-11-21	7
2020-11-25	1

Author:	ManickaP
Assignees:	-
Labels:	area-System.Net.Http
Milestone:	-

[wfurt]

LGTM

[stephentoub]

We might hold this PR back for a few more days to confirm this.

We should still disable it until it can be investigated further; it may not be failing as frequently as it was, but it's still failing.

Thanks.

[wfurt]

/backport to release/5.0

[github-actions]

Started backporting to release/5.0: https://github.com/dotnet/runtime/actions/runs/395324929