test: Fix small typo
Optimize statting a directory

This patch batches the operations for statting and getting the times
for a directory, improving the whole stat method's performance.
Use RadosFsIOSP in RadosFsPriv.hh

Use the mentioned typedef instead of the longer declaration.
Add a pointer to RadosFs in RadosFsPriv

This will be useful when we need to call functions from the public
object.
Abstract the creation of RadosFsIO in a new method

This new method (getOrCreateFsIO) creates the new RadosFsIO in case
it doesn't exist which makes it a more convenient function.

This patch also replaces the creation of the RadosFsIO in RadosFsFile
by this new method.