Remove code related to the rails test command

Remove the mention about this command in the rails command's help
message and remove the "t" alias related to it.
Merge pull request #11050 from robin850/remove-rails-test-mention

Remove code related to the rails test command
flatten merged join_values before building the joins

fixes #10669

While joining_values special treatment is given to string values.
By flattening the array it ensures that string values are detected
as strings and not arrays.
add explicit AS dependencies for ActiveModel::Naming

There are two missing ActiveSupport dependencies to use ActiveModel::Name class or ActiveModel::Naming module independently.

Missing dependencies for Module#delegate defined in `active_support/core_ext/module/delegation`, used at [L148](https://github.com/rails/rails/blob/master/activemodel/lib/active_model/naming.rb#L148)

Missing dependencies for Object#blank? defined in `active_support/core_ext/object/blank`, used at [L131](https://github.com/rails/rails/blob/master/activemodel/lib/active_model/naming.rb#L131)
Merge pull request #10796 from neerajdotname/10669

flatten merged join_values before building the joins
Merge pull request #11053 from yangchenyun/mine

Add explicit dependencies of ActiveSupport to enable independent usage of ActiveModel::Name
test-case to prevent regressions on `Association#build` with an Array.

Closes #11026
Revert "Merge pull request #11053 from yangchenyun/mine"

Those two files are required by active_support/rails.rb
loaded in active_model.rb

It is common to require common dependencies on the root
files to avoid boilerplate in each file.

This reverts commit 763635e30f17800ebc0a8ae98d780edc8ebfb4e5, reversing
changes made to 4f46ef36aaef217834f3f96d3689d32f6a6761ea.
Change a way ActiveRecord's config is prepared for rake tasks

In commit d1d7c86d0 I moved setting migrations paths into activerecord's
railtie to remove Rails dependency on databases.rake. However, it
introduced a regression, ENGINE_PATH was not available at the moment, so
engine's migrations where not added properly to paths. Fix was added
at 97a4a771, but it changes a way things work from using ENGINE_PATH to
APP_RAKEFILE. Additionally, the config runs when the code loads, while
previously it ran in the db:load_config rake task

In order to make it more in pair with original version this commit
changes the config to run only on load_config task. This code uses the
fact that defining a task in rake does not overwrite, but only appends.

It also allows to get back to checking for ENGINE_PATH
Setup env and seed_loaded for DatabaseTasks outside load_config

Those vars can be used in tasks, which not call load_config.
replace all older rocket sign to new ":" from examples of active record and active models
Merge pull request #11067 from rajars2576/fix_older_rocket

replace all older rocket sign to new ":" from examples of active record ...
test-case to prevent regressions described in #10901.