parallels: build with parallels SDK
    
    Executing prlctl command is not an optimal way to interact with
    Parallels Cloud Server (PCS), it's better to use parallels SDK,
    which is a remote API to paralles dispatcher service.
    
    We prepared opensource version of this SDK and published it on
    github, it's distributed under LGPL license. Here is a git repo:
    https://github.com/Parallels/parallels-sdk.
    
    To build with parallels SDK user should get compiler and linker
    options from pkg-config 'parallels-sdk' file. So fix checks in
    configure script and build with parallels SDK, if that pkg-config
    file exists and add gcc options to makefile.
    
    Signed-off-by: Dmitry Guryanov <dguryanov@parallels.com>