add test case to install gcc before golang

observed during build of reproducer docker images:

    Running transaction
      Installing : golang-src-1.2.2-7.fc20.noarch                              1/52
      Installing : golang-pkg-bin-linux-amd64-1.2.2-7.fc20.x86_64              2/52
      Installing : golang-1.2.2-7.fc20.x86_64                                  3/52
      Installing : golang-pkg-linux-amd64-1.2.2-7.fc20.noarch                  4/52
    # runtime/cgo
    exec: "gcc": executable file not found in $PATH
    warning: %post(golang-pkg-linux-amd64-1.2.2-7.fc20.noarch) scriptlet failed, exit status 2
    Non-fatal POSTIN scriptlet failure in rpm package golang-pkg-linux-amd64-1.2.2-7.fc20.noarch
      Installing : mpfr-3.1.2-4.fc20.x86_64                                    5/52