Update documents according to the change of test suite class name

[hogimn]

Proposed Changes

In commit 52201b0, I saw the class names of test suite were changed

ex)
ClientTests -> ClientTestSuite
FunctionalTests -> FunctionalTestSuite
ServerTests -> ServerTestSuite

But, documentations (README.md, RUNNING_TEST.md) have not been updated about this change.
Thus, I made this commit!

Types of Changes

• Bugfix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (correction or otherwise)
• Cosmetics (whitespace, appearance)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating
the PR. If you're unsure about any of them, don't hesitate to ask on the
mailing list. We're here to help! This is simply a reminder of what we are
going to look for before merging your code.

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments

It is a simple document update. Thank you!

[michaelklishin]

Thank you, great catch.