updated tests for node_at_link_head+tail in test_init.py
updated tests for node_at_link_head+tail in test_init.py

cmshobe/landlab,SiccarPoint/landlab,ManuSchmi88/landlab,amandersillinois/landlab,laijingtao/landlab,amandersillinois/landlab,Carralex/landlab,ManuSchmi88/landlab,Carralex/landlab,SiccarPoint/landlab,RondaStrauch/landlab,csherwood-usgs/landlab,csherwood-usgs/landlab,landlab/landlab,landlab/landlab,laijingtao/landlab,cmshobe/landlab,RondaStrauch/landlab,cmshobe/landlab,Carralex/landlab,RondaStrauch/landlab,ManuSchmi88/landlab,landlab/landlab