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This change also:
 - adds x86/x86_64 in the list of supported ABIs.
 - adjusts the regexp of the REST endpoints to support the emulator:
   the old regex was using \w+ to match the device serial, which
   doesn't work with the cases such as "emulator-1234".

TBR=primiano@chromium.org
BUG=

Review URL: https://codereview.chromium.org/887583004

Cr-Commit-Position: refs/heads/master@{#314396}