Implemented all the logic to handle truncate operation.

Test: added truncate test

puts has nothing to do with the FS. thus we leave libc handling it
directly

Ensure that the parent directory exists before to make a new node

mkdirat is not yet supported at the moment.

As usual we should log error and return ENOTSUP

command like cp are relying on the dev_no and ino_num to monitor if the
file have been changed during the copy operation.

dev_no was not properly set, thus it was random. Now it is always 0/0

fcntl now is intercept and support the F_GETFD/F_SETFD command.

opendir need to check that the given path is actually a directory
before to open it.

Moreover now open can be called with the O_DIRECTORY flag in order to
open an existent directory

The `cp` command double check the inode number to detect file changes
during transfers, we need to set it properly and keep it consistent.

inode(file) = std::hash(file_path)

In the daemon read handler manage read beyond end of file as normal case
and not exceptional

According to the read manpage a read could return less bytes then
requested due to an interrupt or an error.

We now try to repeat the read operation until all the existent data have
been read correctly.

It is possible that we read less bytes then requested cause the actual
file doesn't have so much.

The ChunkStorage class now store the chunksize in order to perform
runtime checks upon chunks bundaries.

use mercury automatic SM routing

See merge request zdvresearch_bsc/adafs!87

Mercury now support shared memory autorouting.

A single margo instance can be initialized and it will handle both
shared memory communication and remote ones.

If the endpoint of the RPC is local mercury will automatically use
shared memory.

Since there is only one margo instance all the duplicated code for
rpc/ipc have been unified and simplified considerably.

------

The way in which client contact the server has changed.

 - Server initializes its own margo instance and generate the endpoint
communication string using `HG_Addr_self`.
 - This endpoint description string is written on the pid file
 - When the client library loads it will fetch the server endpoint
description from the pid file and will use that to contact the server.

bugfix: compile mercury with last CMake version available

See merge request zdvresearch_bsc/adafs!85