#2132 - lint and fix with ale#command#Run

A new function is added here which will later be modified for public use
in linter and fixer callbacks. All linting and fixing now goes through
this new function, to prove that it works in all cases.

test/test_lint_on_enter_when_file_changed.vader

@@ -50,6 +50,7 @@ Execute(The file changed event function should set b:ale_file_changed):
 Execute(The file changed event function should lint the current buffer when it has changed):
   set filetype=foobar
   call ale#events#FileChangedEvent(bufnr(''))
+  call ale#test#FlushJobs()
 
   AssertEqual [{
   \   'bufnr': bufnr(''),
@@ -68,6 +69,7 @@ Execute(The buffer should be checked after entering it after the file has change
 
   set filetype=foobar
   call ale#events#ReadOrEnterEvent(bufnr(''))
+  call ale#test#FlushJobs()
 
   AssertEqual [{
   \   'bufnr': bufnr(''),