Add --upstream-branch option

[andre-rosa]

No description provided.

[allenh1]

Overall this is looking pretty good. Left a note inline, but it is mostly a nit-pick.

Before this is merged, though, I'd really like to see some test cases introduced for the added option. If we want to, though, we can just create an issue for it after we merge this PR (since I'm not quite sure how in-depth those tests should go).

[allenh1]

Coverage report for this branch:

Name                                               Stmts   Miss  Cover   Missing
--------------------------------------------------------------------------------
superflore/CacheManager.py                            20      0   100%
superflore/PackageMetadata.py                         22      0   100%
superflore/TempfileManager.py                         34      6    82%   48-56
superflore/__init__.py                                10      4    60%   5-8
superflore/docker.py                                  78     22    72%   42, 56-69, 75, 93-95, 102, 107-108, 119, 121-127
superflore/exceptions.py                              18      2    89%   33, 38
superflore/generate_installers.py                     65      2    97%   46-47
superflore/generators/__init__.py                      0      0   100%
superflore/generators/bitbake/__init__.py              3      1    67%   3
superflore/generators/bitbake/gen_packages.py        102     79    23%   40-122, 129-168, 175-183, 189
superflore/generators/bitbake/ros_meta.py             32     23    28%   26-30, 33-38, 41-54, 57-58
superflore/generators/bitbake/run.py                 123    100    19%   41-201
superflore/generators/bitbake/yocto_recipe.py        118     99    16%   44-67, 70-74, 77-89, 92-96, 99-101, 104-105, 113-116, 125-184
superflore/generators/ebuild/__init__.py               3      1    67%   3
superflore/generators/ebuild/ebuild.py               185     19    90%   96-99, 126-131, 146, 176-180, 186, 193, 206-210
superflore/generators/ebuild/gen_packages.py         140    113    19%   46-119, 125-137, 143-188, 193-210, 213, 216
superflore/generators/ebuild/metadata_xml.py          33      0   100%
superflore/generators/ebuild/overlay_instance.py      45     33    27%   29-34, 37-47, 52-75, 78-79
superflore/generators/ebuild/run.py                  119     97    18%   40-188
superflore/parser.py                                  15      0   100%
superflore/repo_instance.py                           70     51    27%   31-52, 59-68, 71-79, 85-86, 92, 98-99, 105, 108-123, 126
superflore/rosdep_support.py                          37      3    92%   44, 88-89
superflore/test_integration/__init__.py                0      0   100%
superflore/test_integration/gentoo/__init__.py         3      1    67%   3
superflore/test_integration/gentoo/build_base.py      28     19    32%   26-28, 33, 38-54
superflore/test_integration/gentoo/main.py            32     26    19%   24-80
superflore/utils.py                                  191     34    82%   57-60, 64-78, 82-93, 108, 217-218, 222, 231, 235, 237, 239, 241, 243, 245, 247, 249
--------------------------------------------------------------------------------
TOTAL                                               1526    735    52%

Still looking pretty good overall! @tfoote I don't think this affects it much, so I'm going to go ahead and approve this one.

I'll leave it to you to merge it.

[allenh1]

left some optional suggestions. lgtm

[allenh1]

lgtm