Fix bug where apply -d was using parent dir.

[lkysow]

• Fixes Run apply only for a specific project in a multiproject repo #22. We were running apply in the parent directory.
• Also changes error message if no plans are found to apply.

[codecov]

Codecov Report

Merging #23 into master will not change coverage.
The diff coverage is 0%.

@@          Coverage Diff           @@
##           master     #23   +/-   ##
======================================
  Coverage    64.1%   64.1%           
======================================
  Files          38      38           
  Lines        1836    1836           
======================================
  Hits         1177    1177           
  Misses        605     605           
  Partials       54      54

Impacted Files	Coverage Δ
server/events/apply_executor.go	0% <0%> (ø)	⬆️

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