feat(openssl): openssl list -commands, not help

[yedayak]

In #1256 we started parsing the help output. Get the list instead from the openssl list -commands command.

This also stops completing the encryption and digest algorithms, since those are usually used with the enc and dgst subcommands.

Suggested-By: Michael Newton
Fixes: #1324

[yedayak]

The openssl list subcommand doesn't seem to exist in the version shipping with centos7, OpenSSL 1.0.2k-fips 26 Jan 2017

[miken32]

It doesn't exist in the version that shipped with CentOS 4, 5, or 6 either? CentOS 7 is long EOL and anyone still using openssl 1.0 likely aren't keeping their bash-completion on the bleeding edge.

But hey if you're willing to fight with sed to make it work, I won't complain!