qemu: command: Don't generate alias for TLS private key password secret

qemu: command: Don't generate alias for TLS private key password secret

qemuBuildTLSx509CommandLine has no business guessing which alias should
be used. The alias needs to be passed in.

Note that there's a lingering bad design of this, since the secret
object alias is based on the device name and not on the fact that the
secret is used for decrypting of the TLS private key. If we ever add
authentication for chardevs this will bite us.

Thankfully disk code does not support encrypted private keys for TLS so
it can be happily refactored there.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>