armclang-ubl.sh: Add retry logic with exponential backoff

Given that we get regular and apparently non-deterministic HTTP 500 error
codes with TF-M builds (somehow doesn't seem to happen with TF-A builds
though).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I6ec3deff2572a6e9a8617c8110201464cb21e7a8
1 file changed