Build script improvements

Small improvements to the build script:
- Refactor the local build to improve clarity of build output
- Improve error handling
- Detect the geard source path within GOPATH
- Portability fixes
- Fix Docker build
Deploy command requires systemd init
Merge pull request #64 from jwforres/deploy_needs_systemd

Deploy command requires systemd init
Merge pull request #62 from ironcladlou/build-improvements

Build script improvements
Fix geard image tag reference
Merge pull request #66 from ironcladlou/gear-image-tag-fix

Fix geard image tag reference