build, fix and install DC gem manually

`gem install deltacloud' would fail with dependency mismatch:
    deltacloud-core requires
        excon < 0.17.0, >= 0.14.2
        fog >= 1.4.0
    fog---since 4 April '13---requires excon (~> 0.20)
so patch the gemspec to use the previous version of fog
save DC log to (synced) file