env/corellium: use go install to build buildlet
env/corellium: use go install to build buildlet

The environment bootstrap toolchain should use 1.16 or higher.
When setting up a new builder environment, the previous go get
will fail from the current supported toolchain for installing
buildlet command. Use "go install" instead.

Change-Id: Ie5642e9d91389760f22cb439f47ac4280a4561c4
Reviewed-on: https://go-review.googlesource.com/c/build/+/369234
Reviewed-by: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

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