Add a method to get a process parameter.
Add a method to get a process parameter.

This will only match the first process as we don't really know how to
aggregate the results. A parameter can be anything accepted as `-o` flag
of `ps`. For example `pid`, `args` and `vsz` are valid parameters.

chorrell/specinfra,stoned/specinfra,stefanhorning/specinfra,thenexus6/specinfra,minimum2scp/specinfra,yui-knk/specinfra,tacahilo/specinfra,seroron/specinfra,edolnx/specinfra,hidehide55/specinfra,serverspec/specinfra,cosmo0920/specinfra,mizzy/specinfra,murank/specinfra,linyows/specinfra,chinthakagodawita/specinfra,tak7iji/specinfra,doc75/specinfra,afiune/specinfra,uroesch/specinfra,zakkie/specinfra,naga2raja/specinfra,optimizely/specinfra,hfm/specinfra,ryotarai/specinfra,nurse/specinfra,elibus/specinfra,evertrue/specinfra,ihassin/specinfra,apenney/specinfra,sergueik/specinfra,glenux/contrib-specinfra,ChristianKoehler/specinfra,dhoer/specinfra,higanworks/specinfra,elmundio87/specinfra,chiastolite/specinfra,aibou/specinfra,sean-horn/specinfra,lurdan/specinfra,bodgit/specinfra,sonots/specinfra,k0kubun/specinfra,gh2k/specinfra,hideyuki/specinfra,r7kamura/specinfra,tarr1124/specinfra,RoboticCheese/specinfra,tagomoris/specinfra,mactkg/specinfra,yujinakayama/specinfra,miketheman/specinfra,hanazuki/specinfra,3100/specinfra,electrical/specinfra,skamithi/specinfra,verisign/specinfra,chef-partners/specinfra-cisco,pfaffle/specinfra,winebarrel/specinfra,sorah/specinfra