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.