Using a single cache entry for all files of a type is necessary to avoid
overloading the cache service. However, this mechanism is not very efficient
for certain artifacts like wrapper zips and generated-gradle-jars, where the
same individual files are often shared between different jobs.
With this change, any configured file patterns that do not end in '*' will
be cached as individual files. At this time this includes downloaded wrapper
zips and generated-gradle-jars.
Fixes#78
