Implement parallel find
test: Add unit tests for the find method
Call sync before destroying RadosFsIO

In order to avoid leaks.
Fix leak when deleting a pool
Fix memory issue when getting the stored link path

The char * outputted would not get the null char, leading to
possible invalid memory reading.
Fix buffer's length when reading the link xattr

It was using the length of the path by mistake and not the real
buffer's path.
Fix memory leak related to the link's URL

It was leaking when checking if the file path existed, the
file was a link and the URL's output parameter was not supplied.
Use the XAttr real length when returning it

In the getXAttrFromPath and getMapOfXAttrFromPath methods.
Return error if the given length of the XAttr is 0

In the getXAttrFromPath method.
build: Find and link Threads module

To correctly link to pthread.
Fix stat functions' missing return statement

In the RadosFsFile and RadosFsDir. It should return a code.
benchmark: Fix wrong print argument type
Make logic ops explicit by including parenthesis

So clang doesn't complain about it.
tools: Fix missing return in the fsck method
build: Make GTest an optional package
build: Only build tests if GTest was found
build: Use variable for the loglevel file name
build: Fix generating the loglevel file