Fix custom config path being ignored during reload

[jacobtomlinson]

When opsdroid reloads it also reloads its config. Currently this is loaded from the default paths even if a custom path was passed in as a cli argument.

This PR passes any custom paths through to opsdroid for use when reloading.

[codecov]

Codecov Report

Merging #1476 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1476   +/-   ##
=======================================
  Coverage   99.90%   99.90%           
=======================================
  Files          52       52           
  Lines        3184     3186    +2     
=======================================
+ Hits         3181     3183    +2     
  Misses          3        3           

Impacted Files	Coverage Δ
opsdroid/cli/start.py	100.00% <100.00%> (ø)
opsdroid/core.py	100.00% <100.00%> (ø)

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