ast_tls_cert: Add option to skip passphrase for CA private key.

ast_tls_cert: Add option to skip passphrase for CA private key.

Currently, the ast_tls_cert file is hardcoded to use the -des3 option
for 3DES encryption, and the script needs to be manually modified
to not require a passphrase. Add an option (-e) that disables
encryption of the CA private key so no passphrase is required.

Resolves: #1064
(cherry picked from commit eca4ec6b5ea29a7ab9a67fb21fbe0b93b214c9f1)