MODIS merging support

Squashed commit of the following:

commit 76ad8de8
Author: Bruce Flynn <brucef@ssec.wisc.edu>
Date:   Thu May 6 15:37:10 2021 -0500

    test, then push

commit e3a51b48
Author: Bruce Flynn <brucef@ssec.wisc.edu>
Date:   Thu May 6 15:31:48 2021 -0500

    rdrgen Fix attr comparison issues, support additional mission names

commit bb6b5e6d
Author: Bruce Flynn <brucef@ssec.wisc.edu>
Date:   Thu May 6 14:11:49 2021 -0500

    modis merging working and tested

commit 58143956
Author: Bruce Flynn <brucef@ssec.wisc.edu>
Date:   Wed May 5 13:13:23 2021 -0500

    fix bad attr

commit f3bdd86d
Author: Bruce Flynn <brucef@ssec.wisc.edu>
Date:   Wed May 5 11:21:20 2021 -0500

    add module for EOS utils

commit b18d65bb
Author: Bruce Flynn <brucef@ssec.wisc.edu>
Date:   Wed May 5 11:20:59 2021 -0500

    merge: support aqua by using seqid in pointer