Close issue on merge

[prarit]

cmd/mr_create.go: Add --close-issue option

Add an option that allows a user to specify issues that can be closed when
the merge request is merged.  The --close-issue option can be used
multiple times to indicate multiple issues.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>

close #844

[codecov[bot]]

Codecov Report

Patch coverage: 56.52% and project coverage change: +0.31 :tada:

Comparison is base (cce34e2) 55.25% compared to head (971b5b7) 55.57%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #871 +/- ## ========================================== + Coverage 55.25% 55.57% +0.31% ========================================== Files 82 82 Lines 5961 5988 +27 ========================================== + Hits 3294 3328 +34 + Misses 2380 2371 -9 - Partials 287 289 +2 ``` | [Impacted Files](https://app.codecov.io/gh/zaquestion/lab/pull/871?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann) | Coverage Δ | | |---|---|---| | [cmd/mr\_show.go](https://app.codecov.io/gh/zaquestion/lab/pull/871?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann#diff-Y21kL21yX3Nob3cuZ28=) | `65.80% <0.00%> (-1.52%)` | :arrow_down: | | [cmd/mr\_create.go](https://app.codecov.io/gh/zaquestion/lab/pull/871?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann#diff-Y21kL21yX2NyZWF0ZS5nbw==) | `70.04% <59.09%> (-2.00%)` | :arrow_down: | ... and [3 files with indirect coverage changes](https://app.codecov.io/gh/zaquestion/lab/pull/871/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann)

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[bmeneg]

@prarit, the code rearrangement seems odd. Only func init() is left as the final function, the command creation has been the first bit after lib imports and global var declaration, doesn't it?

[zampierilucas]

@bmeneg I agree, on newly created function we use Run: func(... , so it might be nice to also add it here, since you moving it