Improve regexp to prevent false positives
If a filename happened to contain "db" and enough "rwx" characters before, then
this test would previously fail. For example:
```
drwxr-xr-x gitlab-runner/gitlab-runner 0 2015-04-02 07:46 uploads/tmp/cassidy.stokes8477/gitlabhq/36d972fa55d6b44810fc6fd843473adb/
```
Adding a space before the "db" match string tightens up the regexp and reduces the
chance of an unintended match.
See merge request !489
If a filename happened to contain "db" and enough "rwx" characters before, then
this test would previously fail. For example:
```
drwxr-xr-x gitlab-runner/gitlab-runner 0 2015-04-02 07:46 uploads/tmp/cassidy.stokes8477/gitlabhq/36d972fa55d6b44810fc6fd843473adb/
```
Adding a space before the "db" match string tightens up the regexp and reduces the
chance of unintended match.
DEPRECATION: `expect { }.not_to raise_error(SpecificErrorClass)` is deprecated. Use `expect { }.not_to raise_error` (with no args) instead. Called from /home/travis/build/gitlabhq/gitlabhq/spec/tasks/gitlab/backup_rake_spec.rb:42:in `block (4 levels) in <top (required)>'.
