cmd/scollector: fix pseudo file system checking for dfstat on linux
cmd/scollector: fix pseudo file system checking for dfstat on linux

Use string equality testing instead of sub-string matching in the
readLine() function for /proc/filesystems in isPsenduFS(), because the
latter could produce false-positive result.

For a real example:
nodev	selinuxfs
	xfs
these two lines will make the old code think xfs is a pseudo file
system.

closes #1462

simnv/bosun,melifaro/bosun,jareksm/bosun,alienth/bosun,seekingalpha/bosun,alienth/bosun,augporto/bosun,melifaro/bosun,melifaro/bosun,TrentScholl/bosun,seekingalpha/bosun,noblehng/bosun,augporto/bosun,TrentScholl/bosun,simnv/bosun,bookingcom/bosun,bookingcom/bosun,GROpenSourceDev/bosun,mhenderson-so/bosun,mhenderson-so/bosun,Skyscanner/bosun,alienth/bosun,augporto/bosun,CheRuisiBesares/bosun,leapar/bosun,csmith-palantir/bosun,TrentScholl/bosun,seekingalpha/bosun,GROpenSourceDev/bosun,TrentScholl/bosun,leapar/bosun,bookingcom/bosun,bosun-monitor/bosun,melifaro/bosun,jareksm/bosun,noblehng/bosun,bosun-monitor/bosun,Skyscanner/bosun,noblehng/bosun,bosun-monitor/bosun,csmith-palantir/bosun,leapar/bosun,simnv/bosun,bosun-monitor/bosun,Skyscanner/bosun,jareksm/bosun,simnv/bosun,leapar/bosun,CheRuisiBesares/bosun,CheRuisiBesares/bosun,mhenderson-so/bosun,simnv/bosun,jareksm/bosun,mhenderson-so/bosun,Skyscanner/bosun,noblehng/bosun,augporto/bosun,seekingalpha/bosun,jareksm/bosun,CheRuisiBesares/bosun,seekingalpha/bosun,CheRuisiBesares/bosun,TrentScholl/bosun,jareksm/bosun,leapar/bosun,csmith-palantir/bosun,Skyscanner/bosun,bookingcom/bosun,seekingalpha/bosun,alienth/bosun,bosun-monitor/bosun,leapar/bosun,mhenderson-so/bosun,noblehng/bosun,csmith-palantir/bosun,alienth/bosun,GROpenSourceDev/bosun,TrentScholl/bosun,augporto/bosun,Skyscanner/bosun,alienth/bosun,GROpenSourceDev/bosun,melifaro/bosun,bookingcom/bosun,noblehng/bosun,simnv/bosun,bosun-monitor/bosun,csmith-palantir/bosun,bookingcom/bosun,mhenderson-so/bosun,GROpenSourceDev/bosun,augporto/bosun,CheRuisiBesares/bosun,GROpenSourceDev/bosun,csmith-palantir/bosun,melifaro/bosun