List: capture git errors for local workflows

[ewels]

Handle exceptions due to detached HEAD refs in the local pulls of remote workflows.
Prints a helpful message about how to fix.

Fixes #297

$ nf-core list

                                          ,--./,-.
          ___     __   __   __   ___     /,-._.--~\
    |\ | |__  __ /  ` /  \ |__) |__         }  {
    | \| |       \__, \__/ |  \ |___     \`-._,-`-,
                                          `._,._,'


ERROR: Could not fetch status of Nextflow copy of nf-core/chipseq:
   HEAD is a detached symbolic reference as it points to '3207ff80b2cf8034b97cf1b6f054581e9b1b10f9'

It's probably a good idea to delete this local copy and pull again:
   rm -rf /Users/ewels/.nextflow/assets/nf-core/chipseq
   nextflow pull nf-core/chipseq

Name                       Version    Released       Last Pulled    Have latest release?
-------------------------  ---------  -------------  -------------  ----------------------
nf-core/smrnaseq           1.0.0      2 weeks ago    -              -
nf-core/mhcquant           1.3        2 months ago   -              -
nf-core/ampliseq           1.1.0      3 months ago   -              -
nf-core/hlatyping          1.1.5      3 months ago   8 months ago   No
nf-core/eager              2.0.7      4 months ago   -              -
nf-core/chipseq            1.0.0      4 months ago                  No
nf-core/rnafusion          1.0.2      5 months ago   6 months ago   No
[...]

[drpatelh]

Nice 👍

[ewels]

Travis passing ✅

[drpatelh]

Merge conflict here now 😅

[ewels]

Bloody changelog 😆

[ewels]

I guess this serves me right for opening so many PRs in parallel... 🤦‍♂

[drpatelh]

💥