Initialise $UCC_VERBOSE in run_tests
Initialise $UCC_VERBOSE in run_tests

To avoid test logs looking like:
```
Use of uninitialized value $ENV{"UCC_VERBOSE"} in numeric gt (>) at ./run_tests line 172.
```

bobrippling/ucc-c-compiler,bobrippling/ucc-c-compiler,bobrippling/ucc-c-compiler