misc/reboot: skip TestRepeatBootstrap on short builders

This test is slow and resource-intensive, and will rarely catch
failures. It is important to run sometimes, but probably a waste of
time on smaller (and especially reverse) builders.
Rather than hard-coding a list of small builders, only run it on the
longtest builders.

Fixes golang#35233
Fixes golang#30892
Fixes golang#49753

Change-Id: I25a9702e1f541246ea200fd7c79414ca5f69edae
Reviewed-on: https://go-review.googlesource.com/c/go/+/366538
Trust: Bryan C. Mills <[email protected]>
Run-TryBot: Bryan C. Mills <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: Bryan C. Mills

misc/reboot/reboot_test.go

@@ -15,6 +15,10 @@ import (
 )
 
 func TestRepeatBootstrap(t *testing.T) {
+	if testing.Short() {
+		t.Skipf("skipping test that rebuilds the entire toolchain")
+	}
+
 	goroot, err := os.MkdirTemp("", "reboot-goroot")
 	if err != nil {
 		t.Fatal(err)