Ignore errors when closing an old caching backend.

Review Request #8625 — Created Jan. 16, 2017 and submitted — Latest diff uploaded

Information

Djblets
release-0.8.x
ad1c9ec...

Reviewers

When enabling new cache backend configuration, it was possible to hit an
error closing the old backend, breaking the entire loading process. This
meant that some bad default configuration would prevent a new good
configuration from being used.

We now ignore any errors encountered from closing the old backend.

Tested with a bad configuration being swapped out. I was still able to
load in the new configuration and continue on.