When creating backup tar files, only change permissions on the `db`,
`uploads`, and `repositories` directories, not their contents.

Change permissions on backup files - #2

Use more restrictive permissions for backup tar files and for the db, uploads, and repositories directories inside the tar files.  See #1894.  Now the backup task recursively `chmod`s the `db/`, `uploads/`, and `repositories/` folders with 0700 permissions, and the tar file is created as 0600.

This is a followup to !1703, which was reverted because it broke Rspec tests.  The test failures were due to the rake task changing directories and not changing back, which I fixed with this commit.

cc @sytse

See merge request !1716

Use more restrictive permissions for backup tar files and for the db,
uploads, and repositories directories inside the tar files.

This reverts commit c42262b43b009af990e5769840391862d64a1c2d, reversing
changes made to c6586b1283a94c8f08bc669f4d8a9384b263073e.

Use more restrictive permissions for backup tar files and for the db,
uploads, and repositories directories inside the tar files.

This reverts commit 7d5f86f6cbd187e75a6ba164ad6bfd036977dd07.