Ignore exceptions while resolving placeholders in PropertySources

When a PropertySourcesPropertyValues is used to bind Environment
values to a bean (or the SpringApplication) it tries to resolve
placeholders eagerly in the Environment. Any that fail might not
actually be a problem for users (until validation is done it's
impossible to tell even whether that value was needed for the
ongoing binding or not).

Fixed by ignoring exceptions in the PropertySourcesPropertyValues
constructor.

Fixes gh-108