Improvements to phpunit testing suite

[Nathan Lewis]

This patch refactors how test users are created, now create_test_user, and add two new data generators, create_test_group and create_test_institution. The exists tests were updated to use the new create_test_user function. create_test_group and create_test_institution are currently unused (I've been using them in as-yet unsubmitted patches).

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/3261

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/3261
Committed: http://gitorious.org/mahara/mahara/commit/73f9396ec2daea22b79767faf3598a797716d1d4
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit 73f9396ec2daea22b79767faf3598a797716d1d4
Author: Nathan Lewis <email address hidden>
Date: Tue Apr 15 13:52:28 2014 +1200

Add some data generator funtions to phpunit testing suite (Bug #1307777)
- Replaces require_user and require_test_user with create_test_user
- Added create_test_group and create_test_institution

Change-Id: I8f2acbeef986943cbb4712f47226456fdf3d9570
Signed-off-by: Nathan Lewis <email address hidden>
Signed-off-by: Yuliya Bozhko <email address hidden>