tests: Start tests for 4k storage
    
    We added API for using 4k sector size and various alignments, but there
    are no tests for the new APIs with disks using 4k sector size. Testing
    this is complicated since creating a block device and mounting file
    systems requires root, and we like to run the tests as a regular user.
    
    Add new tests for writing and reading lockspace and resource using 4k
    storage provided by the user. If a path is not specified the tests are
    skipped.
    
    To run the tests, you need to create a block device using 4k sector size
    and optionally create a file system and mount it. The process is
    explained in README.dev.
    
    Then pass the path of the block device or file on the new file system to
    the tests:
    
        USER_4K_PATH=/dev/loop2 tox -e py27
    
    Adding and removing lockspace and acquiring resources is not tested yet
    with 4k storage.
    
    Signed-off-by: Nir Soffer <nsoffer@redhat.com>