For jdk8u aarch32|alpine beta triggers check for existance of a specific asset

[andrew-m-leonard]

Fixes #1152

Update trigger_beta_build.groovy to check for the existence of a specific asset rather than rely purely on the release tag existing.

• x64_linux : Main versions
• arm_linux : jdk8u_aarch32
• x64_alpine-linux : jdk8u_x64_alpine

Also prevent evaluation pipelines incorrectly triggering for jdk8u_aarch32 and jdk8u_alpine.

Note: This change will imply that if the given "arch" above is failing to build, then repeat triggers can occur in that scenario, but then there's obviously a build problem anyway...

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[adamfarley]

LGTM

[adamfarley]

Linter requests 2 changes. Thoughts?

[adamfarley]

LGTM

[steelhead31]

Looks good.