UserServiceTest: get rid from using a few global constants.

No functional changes.
Extracted method UserServiceTest.getValidUser() -> TestObjects.createUser()

No functional changes.
SiteServiceTest: replaced own method to using TestObjects.createUser()

No functional changes.
SiteServiceTest: fixed a typo in test methods names.

Corrections for d14c11f1b1d4442bd97838e9c5f2381aa66d38c3 commit.

Found by Intellij IDEA's spell checker.

No functional changes.