Drops the build stage in Gitlab CI tests and includes build in the test
jobs. Building in a separate stage did not work as intended. The test
jobs rebuilt Kvazaar without the CFLAGS given in the build jobs and
overwrote the results from the build jobs. The test were therefore run
without the sanitizers enabled.
Enables build and test with AddressSanitizer, ThreadSanitizer and
UndefinedBehaviorSanitizer in Gitlab CI configuration. The LeakSanitizer
component of AddressSanitizer is disabled because ptrace cannot be used
inside the container.