syscall: relax output check in TestGroupCleanupUserNamespace
syscall: relax output check in TestGroupCleanupUserNamespace

“If you have a procedure with ten parameters, you probably missed some.”
― attr. Alan J. Perlis

I argue that the same is true for hard-coded special cases.

In TestGroupCleanupUserNamespace, instead of a curated list of strings
observed in the wild we now check for a prefix, as was done for
TestGroupCleanup in CL 24670.

Updates #16224.
Updates #16303.
Updates #19938.
Updates #34547.
Updates #46752.
Fixes #52088.

Change-Id: I59c5b0c048113e306996c0f8247e09c714d2423a
Reviewed-on: https://go-review.googlesource.com/c/go/+/397316
Trust: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Run-TryBot: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

nawawi/go,golang/go,golang/go,CAFxX/go,golang/go,nawawi/go,nawawi/go,nawawi/go,golang/go,golang/go,CAFxX/go,golang/go,nawawi/go,nawawi/go,golang/go,CAFxX/go,CAFxX/go,CAFxX/go,CAFxX/go,nawawi/go,CAFxX/go,golang/go,nawawi/go,CAFxX/go