Explicitly list files and dirs included in gem (test_)files

with the catch all approach there were a lot of files included
that do not need to be in the gem. I.e. Jenkinsfile all dot files
and dirs related to CI configuration and rubocop linting ...

This causes problems whe i.e. building rpm packages
where all of these files need to be explicitly excluded.

fog-vsphere.gemspec

@@ -14,8 +14,9 @@ Gem::Specification.new do |spec|
   spec.homepage      = 'https://github.com/fog/fog-vsphere'
   spec.license       = 'MIT'
 
-  spec.files         = `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(tests?|spec|features)/}) }
-  spec.test_files    = spec.files.grep(%r{^tests\/})
+  spec.files = Dir['lib/**/*'] +
+               ['LICENSE.md', 'Rakefile', 'README.md', 'CHANGELOG.md', 'CONTRIBUTORS.md']
+  spec.test_files = Dir['tests/**/*']
 
   spec.require_paths = ['lib']