RuntimeTest and its sublasses are still based on JUnit 3, as they
implement the JUnit 3 TestCase and the Eclipse-specific CoreTest
subclass, respectively. This change migrates those tests in
org.eclipse.core.tests.runtime to JUnit 4 that are neither job tests,
nor session or performance tests.

In total, the change does the following:
- Migrates several tests in org.eclipse.core.tests.runtime to JUnit 4
- Replaces all try-catch constructs with either exceptions thrown by the
test or assertThrows
- Replaces unnecessary custom assert implementations with JUnit 4
asserts or hamcrest matcher calls
- Encapsulates all AutoClosables into try-with-resources blocks