Adding script to create a SRPM
    
    Recommended way to create SRPM is to run make (prerelease-)srpm.
    But in previous case make file have to be generated, therefore
    configure script should not fail. (all sssd required dependencies have to be
    installed)
    Script make_srpm.sh can be runned without running configure, script can be
    runned only from git repository.
    
    https://fedorahosted.org/sssd/ticket/1927