Allow for Android offline mirrors to be executed on developer's laptops

Summary:
Before this change, the only way to update the offline mirror was to run it on a devmachine
(OD won't work either due to network restriction).

Developer's laptop also won't work as they would download AAPT2 for MacOS.
In the offline mirror instead we need AAPT2 for Linux as that's Sandcastle runner type.

This relaxes this requirement so the next time a developer has to update the offline
mirror they will see the message on the diff with the command to execute, and they should
be able to run the command locally (or on their devbox).

Changelog:
[Internal] [Changed] - Allow for Android offline mirrors to be executed on developer's laptops

allow-large-files

Reviewed By: cipolleschi

Differential Revision: D43344651

fbshipit-source-id: 3e91adb2db45cf94d3f947aaab501d98580dc43d