Try starting Omnisharp server without solution file

With this change, ycmd will attempt to start the Omnisharp server with
the current working directory when no solution file is found. The
runtime check for solution file presence is not required and exception
raising is defered to Omnisharp.

ycmd/completers/cs/cs_completer.py

@@ -381,7 +381,13 @@ def _GetSolutionFile( self, filepath ):
       # to be confirmed
       path_to_solutionfile = solutiondetection.FindSolutionPath( filepath )
       if not path_to_solutionfile:
-        raise RuntimeError( 'Autodetection of solution file failed.' )
+        path_to_solutionfile = os.getcwd()
+        LOGGER.info( 'Autodetection of solution file failed, '
+                    'trying current directory ({0}).'
+                    .format( path_to_solutionfile ) )
+      else:
+        LOGGER.info( 'Loading solution file {0}'
+                    .format( path_to_solutionfile ) )
       self._solution_for_file[ filepath ] = path_to_solutionfile
 
     return self._solution_for_file[ filepath ]