Preparing for 4.2.0.beta1 release
Use system /tmp when testing actionpack

https://github.com/rails/rails/commit/c64bff2c87ebf363703c63ecd4a96d56a1a78364
added support and enabled parallel execution of the actionpack tests.

However it introduced https://github.com/rails/rails/commit/c64bff2c87ebf363703c63ecd4a96d56a1a78364
since one cannot connect to a socket file that's inside a Vagrant synced folder
due to security restrictions, and DRb tries to.

Also rename the temporary files to make it obvious that they're rails-related,
since now they're placed outside the project's directory.

Fixes https://github.com/rails/rails/commit/c64bff2c87ebf363703c63ecd4a96d56a1a78364
use self instead of #read_attribute
Fixed Active Job Backburner adapter
Merge pull request #16746 from cristianbica/fix-backburner-adapter

Fixed Active Job Backburner adapter
Merge branch 'master' of github.com:rails/rails
Added yield to Object#presence
Update examples to show real worth
Use instance_eval on @tenderlove's suggestion :trollface:
Clarify the origin of this great addition to Rails :trollface: :trollface :trollface:
We tenderized the wrong method! Object#try already had the yield option, just needed some tenderloving instance_eval to fit the bill
reduce object allocations in utc_offset

`try` allocates an array on every call, we should avoid calling it in
hotspots.  This reduced AttributeMethodsTest#test_setting_time_zone_aware_attribute_with_string
from 18k allocations to 14k
Forgot to set Migration.verbose at f8d9a51949d6f6cfcab7cc7d501e137836eb88dc :bomb:
Bring back the test cases for `presence`

This was removed by mistake in 5e51bdd
Merge pull request #16644 from Agis-/drb-tests-actionpack-vagrant

Use system /tmp for temp files when testing actionpack
Refer to the library name instead of the constant

When we are loading a component and we want to know its version, we are
actually not speaking about the constant but the library itself.

[ci skip]

[Godfrey Chan & Xavier Noria]
[ActionMailer] Rename test/test_test to test/test_case_test
[ci skip] add line about text layout
AR#reset_column_information sometimes queries via table_exists?

so this assertion causes random test fail
MySQL: set connection collation along with the charset

Sets the connection collation to the database collation configured
in database.yml. Otherwise, `SET NAMES utf8mb4` will use the default
collation for that charset (utf8mb4_general_ci) when you may have chosen
a different collation, like utf8mb4_unicode_ci.

This only applies to literal string comparisons, not column values, so
it is unlikely to affect you.