Fix ExcludeWatch

The base statement needs to be evaluated. Otherwise the test code will
be skipped incorrectly.

Bug: 207326840
Test: add `assertTrue(false)` to tests
      run `atest android.packageinstaller.install.cts.SessionTest`
      check tests fail as expected

Change-Id: I30bfccbeda4f94d9ef005ce972ca996ed81643ac