fix inconsistency in how PropertyDescriptors that use StandardValidators.BOOLEAN_VALIDATOR are built

There is some inconsistency in how Property descriptors are built when the validator is the BOOLEAN validator, notably with defaultValue and allowableValues

Sometimes this (Upper Case First Character)

                .defaultValue("True")
                .allowableValues("True", "False")
                .addValidator(StandardValidators.BOOLEAN_VALIDATOR)

Sometimes this (all lower case)

            .addValidator(StandardValidators.BOOLEAN_VALIDATOR)
            .allowableValues("true", "false")
            .defaultValue("true")

And sometimes no allowableValues are used.

Discovered when reviewing pull request for NIFI-944 and noticed the author of a pull request attempted to add allowableValues for consistency.