Remove precision qualifiers from booleans in constructor tests

Use default precision qualifiers for float and int instead. Booleans or
literals do not have precision qualifiers.
Add tests for a literal and booleans with a precision qualifier

According to GLSL spec, boolean variables and literals do not
have a precision qualifier, so compilation should fail in these cases.
Merge pull request #500 from NVIDIA/bvec-precision-fix

Fix conformance test issues related to boolean precision