New releases to pick up latest version of google-cloud-core

[liyanhui1228]

Can we release new versions for all the libraries that depending on google-cloud-core? #6835 and #6858 are checked in for updating the dependency version, we just need to release the changes. Depending on an old version would potentially causing version conflicts for users.

e.g trace and bigquery are not compatible with each other: google-cloud-trace 0.20.1 has requirement google-cloud-core<0.30dev,>=0.29.0, but you have google-cloud-core 0.28.1.

[tseaver]

$ git grep -l "google-cloud-core" | grep setup.py
bigquery/setup.py
bigtable/setup.py
core/setup.py
datastore/setup.py
dns/setup.py
firestore/setup.py
logging/setup.py
resource_manager/setup.py
runtimeconfig/setup.py
spanner/setup.py
storage/setup.py
trace/setup.py
translate/setup.py