Modified pbcore.io.base.py so that 'ls' is called in order to 
trigger mount and avoid NFS issues before trying to access a 
file handler.
bug 25376	

[git-p4: depot-paths = "//depot/software/smrtanalysis/bioinformatics/lib/python/pbcore/": change = 139036]
Revert change 139036	
bug 25376

[git-p4: depot-paths = "//depot/software/smrtanalysis/bioinformatics/lib/python/pbcore/": change = 139038]