UCS/VFS: Connect to daemon and expose dummy filesystem

[yosefe]

Why

Infrastructure for exposing UCX internal status over FUSE

How

• UCS starts a FUSE thread which connects to a mount daemon and serves filesystem operations
• If the daemon does not exits, the thread will wait for it to appear, using inotify service

        +-----------------------+
        | filesystem operations |
        | (cat, ls, etc.)       |
        +-----------------------+
                     |
        +------------v-----------+
        |   kernel FUSE driver   |
        +------------------------+
                     ^
                     |
                +----v----+             +---------+
                |         |             |         |
                |  UCS    |             | ucx_vfs |
                |  fuse   +<----------->+ mount   |
                |  thread |             | daemon  |
                |         |             |         |
                +---------+             +---------+

[dmitrygx]

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