utilities: also create latest directory (#2267)
utilities: also create latest directory (#2267)

* utilities: also create latest directory

This commit makes create_site.sh create directory "latest",
containing the docs for the latest release.

This commit also fixes a bug.
Previously, create_site chooses to copy only files in directory
whose names begin with the current version.
Since the current version of google-cloud-java is 0.y.z,
libraries in alpha and beta are copied properly.
However, libraries in GA are not copied, because their versions
are x.y.z where x is not 0.

vam-google/google-cloud-java,FirebasePrivate/google-cloud-java,vam-google/google-cloud-java,shinfan/gcloud-java,mbrukman/gcloud-java,FirebasePrivate/google-cloud-java,FirebasePrivate/google-cloud-java,vam-google/google-cloud-java,vam-google/google-cloud-java,FirebasePrivate/google-cloud-java,mbrukman/gcloud-java,vam-google/google-cloud-java,shinfan/gcloud-java,mbrukman/gcloud-java,shinfan/gcloud-java,vam-google/google-cloud-java,shinfan/gcloud-java,mbrukman/gcloud-java,shinfan/gcloud-java,FirebasePrivate/google-cloud-java