Add `rails test` command to run the test suite

To run the whole test suite:

    $ rails test

To run the test file(s):

    $ rails test test/unit/foo_test.rb [test/unit/bar_test.rb ...]

To run the test suite

    $ rails test [models,helpers,units,controllers,mailers,...]

For more information, see `rails test --help`.

This command will eventually replacing `rake test:*`, and `rake test`
command will actually invoking `rails test` instead.
Update testing documentation

* Update test invocation to use `rails test` instead.
* Update all the test command previews (since we're now using MiniTest.)
* Mentioning MiniTest instead of Test::Unit.
* Update list of test suites.
Add support for MiniTest flags in TestRunner

Any flags that got set will be passed through to MiniTest::Unit.runner,
such as `-n`, `-s-, and `-v`.
Load fixtures only when running suites, or `-f`

* `rails test -f` will run the test suites with all fixtures loaded
* New application will now generated without `fixtures :all` line
  enabled by default.
Improve wording for rails test command
Update Rake tasks to call `rails test` instead

Also, print out deprecation warning for other rake tasks except
`rake test` and `rake` (default)
Make sure that `rails test` load test in test env
document habtm join-table name with custom prefix [ci skip].

Closes #9643.

The logic was introduced with 46492949
Merge pull request #9645 from senny/9643_habtm_wrong_table_name

document habtm join-table name with custom prefix [ci skip]
Address ActiveRecord::StatementInvalid: OCIError: ORA-00979
Change from each to each_value on hash to avoid unused variable warning
Merge pull request #9650 from yahonda/group_by_oracle

Address ActiveRecord::StatementInvalid: OCIError: ORA-00979
Merge pull request #9651 from vipulnsward/change_to_each_value_intest

Change from each to each_value on hash to avoid unused variable warning
Fixed tests for returning an instance of `Time` in the local system timezone.
Merge pull request #9653 from jetthoughts/master

Fixed tests `to_time` returning an instance of `Time` in the local system timezone.

Tests for to_time returning an instance of Time in the local system timezone did not take in account DST when they used mixed timezone declarations like 'US/Eastern' and '-0500'.

Replaced timezone with DST by timezone without DST.
Cleanup tests for unused variables
add an missing assertion to inheritance_test.rb

assertion for
https://github.com/rails/rails/blob/ad624345e54bd20802de67b2b5c9ef29ecf5
d5f4/activerecord/lib/active_record/inheritance.rb#L32
Merge pull request #9658 from tkhr/add-assert-to-test_company_descends_from_active_record

add an missing assertion to inheritance_test.rb
Merge pull request #9657 from vipulnsward/cleanup_tests

Cleanup tests for unused variables
Merge pull request #9080 from sikachu/master-rails-test

Add `rails test` command to run the test suite