fix(bkgpslog):Use eval to build command strings

Use eval to build command strings instead of simply putting bare
unquoted variable. This is necessary because the `recipients` variable
used to build a command to encrypt files may contain quotes if one of
the recipients is an ssh key which may have a space:

    ssh-rsa AAAAB...

This should fix the inability of `bkgpslog` to accept quoted ssh
pubkey strings as a specified `-r` option argument.