[FS#942] openvpn-mbedtls no longer accepts SHA1 certificates

[LEDE Bugs]

The following task has a new comment added:

FS#942 - openvpn-mbedtls no longer accepts SHA1 certificates
User who did this - Baptiste Jonglez (bjonglez)

----------
I understand the rationale, and I'm all for more security.

However, as a LEDE/openvpn user, I probably don't have access to the openvpn server (for instance it might be a commercial VPN provider).  So it is really frustrating to have a broken service without any practical way to fix it.

My main complaint is that it introduces a non-compatible change in lede-17.01.  As a compromise, I think it makes sense to:

- re-enable SHA1 in lede-17.01
- leave SHA1 disabled in trunk
- clearly mention in the release notes of the next LEDE/OpenWRT major release that mbedtls no longer supports SHA1 signatures.
----------

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=942#comment3168