fix mem swap test failing on systems with no swap memory
fix mem swap test failing on systems with no swap memory

end18/psutil,tigerneil/psutil,stupidcache/psutil,stupidcache/psutil,chjwang/psutil,peter-hst/psutil,jucapj/psutil,zhengzheng/psutil,skyshe/psutil,kiranvizru/psutil,marmolu/psutil,AlanZatarain/psutil,google-code-export/psutil,anfedorov/psutil,jucapj/psutil,huson2012/psutil,kiranvizru/psutil,tigerneil/psutil,tigerneil/psutil,huson2012/psutil,djhaskin987/psutil,huson2012/psutil,vmolsa/psutil,creativewild/psutil,creativewild/psutil,djhaskin987/psutil,google-code-export/psutil,anfedorov/psutil,vmolsa/psutil,google-code-export/psutil,Alwnikrotikz/psutil,djhaskin987/psutil,shiva21/psutil,AlanZatarain/psutil,marmolu/psutil,kiranvizru/psutil,Alwnikrotikz/psutil,google-code-export/psutil,peter-hst/psutil,stupidcache/psutil,skyshe/psutil,end18/psutil,PFZheng/psutil,kiranvizru/psutil,end18/psutil,skyshe/psutil,vmolsa/psutil,creativewild/psutil,vmolsa/psutil,djhaskin987/psutil,nmani1905/psutil,PFZheng/psutil,skyshe/psutil,shiva21/psutil,chjwang/psutil,tigerneil/psutil,nmani1905/psutil,zhengzheng/psutil,end18/psutil