Bug 1324040 - mozboot: Download rustup without SNI. r=froydnj

It seems older Python (e.g. 2.7 from Ubuntu 14.04) doesn't
support SNI, so we get a TLS error with the canonical
https://static.rust-lang.org/ url even when using the
`requests` module.

Fall back to the no-CNAME host instead which is ugly but works.

Thanks to Simon Sapin for the suggestion.

MozReview-Commit-ID: I6V5ASijuKi

--HG--
extra : rebase_source : 2e2a449fbb3011b51207f1c6baa3d288d0dc774c

python/mozboot/mozboot/rust.py

@@ -12,7 +12,9 @@ import subprocess
 import sys
 
 # Base url for pulling the rustup installer.
-RUSTUP_URL_BASE = 'https://static.rust-lang.org/rustup'
+# Use the no-CNAME host for compatibilty with Python 2.7
+# which doesn't support SNI.
+RUSTUP_URL_BASE = 'https://static-rust-lang-org.s3.amazonaws.com/rustup'
 
 # Pull this to get the lastest stable version number.
 RUSTUP_MANIFEST = os.path.join(RUSTUP_URL_BASE, 'release-stable.toml')