CA-109295: Allow other_config:hvm_serial to set values other than "pty"

Signed-off-by: John Else <john.else@citrix.com>
Add tests for xapi -> xenopsd HVM metadata conversion

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #1446 from johnelse/ca-109295-pr-1061

Allow other_config:hvm_serial to set values other than "pty"