master: Add support for access ACLs

This commit adds very basic support for access ACLs in the master server.
Some optimizations may be added in the future, eg. deduplication of
ExtendedAcl structures. The master server does not use these ACLs for
permission checks, so to use the mechanism one has to set nomasterpermcheck
session flag.

Change-Id: I24dab4f2093149b17c006817b4d237714612b9cc
common: Add ACL xattr <-> AccessControlList converter

ACL on Linux is stored as serialized struct of kernel in extended attributes,
so it's very inconvenient to use them directly. To allow an easy manipulation
on these data, this commit introduces a class which converts them to an
AccessControlList object (and vice versa). A definition of kernel structs have
been extracted from its sources and adapted to this use in this case.

Change-Id: I7e218ad349db410d0ae1ca42fa7b91bc95fd11f1
mount: ACL support in mastercomm

Implement functions for sending ACL requests to master:
* fs_deletacl
* fs_getacl
* fs_setacl

Change-Id: Ic04dbf4ab84ff62290d84fc726bc29b13fd7d064
mount: Unify handling of unusual xattrs

Simplify the code dealing with custom xattrs (ACL, capabilities, etc.).

Change-Id: I8b904ad57be59693cf4b50c1c277c26967852b7d
mount: Handle Linux ACL xattrs properly

WTF is going to happen on other platforms?

Change-Id: I389c969c18e3c45afdb08bb6e4c1e660769ede7d
utils: Fix dissection of ACL messages in the Wireskark plugin

The right name for a 16-bit field in LIZ_CLTOMA_SETACL and LIZ_MATOCL_GETACL
which represents an access mask is 'mode'. This name is used in
the AccessControlList class and many other messages, ie. CLTOMA_FUSE_MKDIR
or CLTOMA_FUSE_MKNOD.

Moreover, fields named 'mode' are displayed in octal in the Wireshark
interface, which is the expected behavior in case of these two messages.

Change-Id: I939200aef96c80b146f5715a07aad60b9330e128
tests: Enable tests of access ACLs

This commit enables tests of access ACLs. Default ACLs are not implemented yet,
so some parts of the tests are still disabled. By the way some minor flaws
in these tests are fixed.

Change-Id: Ia8237b130dbc3176047dd27c067310fd4708db7d
master: Remove dead code in loading metadata

Change-Id: I4c09a718c4e8853c015ce0b982441615202ead97