Test: Do not close modules twice
Test: Do not close modules twice

Before this change the test would cause a segmentation fault if the
default storage plugin specified a function for `ELEKTRA_PLUGIN_CLOSE`.
This was the case since both `elektraModulesClose` and `kdb_del` close
the default storage plugin. Under this circumstances `kdb_del` would
try to close an already closed plugin and fail.

mpranj/libelektra,BernhardDenner/libelektra,ElektraInitiative/libelektra,ElektraInitiative/libelektra,petermax2/libelektra,petermax2/libelektra,BernhardDenner/libelektra,ElektraInitiative/libelektra,petermax2/libelektra,mpranj/libelektra,mpranj/libelektra,BernhardDenner/libelektra,mpranj/libelektra,mpranj/libelektra,mpranj/libelektra,BernhardDenner/libelektra,petermax2/libelektra,e1528532/libelektra,ElektraInitiative/libelektra,e1528532/libelektra,ElektraInitiative/libelektra,mpranj/libelektra,e1528532/libelektra,e1528532/libelektra,petermax2/libelektra,BernhardDenner/libelektra,ElektraInitiative/libelektra,BernhardDenner/libelektra,e1528532/libelektra,mpranj/libelektra,ElektraInitiative/libelektra,petermax2/libelektra,ElektraInitiative/libelektra,mpranj/libelektra,e1528532/libelektra,ElektraInitiative/libelektra,BernhardDenner/libelektra,e1528532/libelektra,petermax2/libelektra,mpranj/libelektra,mpranj/libelektra,ElektraInitiative/libelektra,BernhardDenner/libelektra,petermax2/libelektra,ElektraInitiative/libelektra,e1528532/libelektra,petermax2/libelektra,BernhardDenner/libelektra