Audit and convert tests to test/unit (minitest)

:construction: WIP :construction: 

This PR converts the RSpec tests to minitest. Most of the tests were translated over, but I'll make inline notes where I modified or removed tests for clarity.

- convert rspec tests to test/unit
- rename 'test/common' to 'test/test_helper'
- remove metaid dependency
- remove rspec dependency
- remove autotest
- auto generate gemspec files manifest

```
$ time ruby test/test_ldap_connection.rb 
/opt/rubies/2.1.2-github1/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- test_helper (LoadError)
	from /opt/rubies/2.1.2-github1/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
	from test/test_ldap_connection.rb:1:in `<main>'
```

This works with `require_relative`, but doesn't work with `require` because `test/` isn't on the path when the current directory is the parent (repo root), running files in the nested directory. `test_helper` *is* relative to the file and doesn't need to depend on the PATH to resolve its location.