Replace x/crypto/pkcs12 with sslmate.com go-pkcs12

[renini]

This fixes error: Pairing failed: err="pkcs12: unknown digest algorithm: 2.16.840.1.101.3.4.2.1"

while using an p12 cert for pairing which is hashed with the sha256 algorithm.

This package is forked from golang.org/x/crypto/pkcs12, which is frozen.