(maint) Use cp -rL when backing up ca directory
(maint) Use cp -rL when backing up ca directory

The `cp -r` command does not follow symlinks. So the command to copy the ssl
directory to `/tmp/ssl-bkp` results in a new symlink being created
`/tmp/ssl-bkp/ca` that points to `/etc/puppetlabs/puppetserver/ca`.

So later the test tries to copy the backup to the destination:

    cp /tmp/ssl-bkp/ca/ca_crl.pem /etc/puppetlabs/puppet/ssl/ca/ca_crl.pem

and it fails because the source and destination files are actually the same
file (inode).

Instead use `cp -rL` which follows symlinks. As a result of the change, the
backup directory contains a copy of the ca directory after following symlinks.

puppetlabs/pxp-agent,puppetlabs/pxp-agent,puppetlabs/pxp-agent