Release 7.7.0

Fixes:

  + The `selinux` configuration steps may sometimes fail. Our customers always end up disabling `selinux`, so remove it.
  + The changelog was obsolete (not up to date); remove it.
  + Submit a bit more data in logging (OS details)
  + Add checks in the install script for both root and supported OS (we received automated error reports for installs attempted on Amazon Linux)
  + Log unexpected errors in the `scalr-manage` script (his has substantial test coverage, but logging those errors really isn't difficult, so it's worth it)
  + Add a `match-version` command to `scalr-manage` that checks whether a suitable configuration already exists on the system (so, if an installation fails, users can run `dist/install.sh` again and we preserve their configuration, but if we push an update, they are prompted to re-create their configuration). This helps if we receive an automated error report that has to do with attributes (like we had with IPv6 detection).
  + Fix a cleanup issue in tests.