[ct] Use vpython when calling metrics_analysis benchmark
[ct] Use vpython when calling metrics_analysis benchmark

Bug: skia:12260
Change-Id: Ic7a23fafd0cd717c51a98c1c9d72135afe915a58
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/436276
Reviewed-by: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

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