cmd/coordinator,internal/gomote: fix release prioritization
cmd/coordinator,internal/gomote: fix release prioritization

Updates the username matching in the coordinator to determine if a
buildlet is for a release.

Updates golang/go#48857

Change-Id: I0d7197ac2955baab2d8b3eb37bb265cf77a43876
Reviewed-on: https://go-review.googlesource.com/c/build/+/422596
Auto-Submit: Jenny Rakoczy <6a3f4389a53c889b623e67f385f28ab8e84e5029@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
Run-TryBot: Jenny Rakoczy <6a3f4389a53c889b623e67f385f28ab8e84e5029@golang.org>

golang/build,golang/build,golang/build,golang/build