virsh.volume: Fix test issues

Resolve multiple issues with the test:

 1. Calling utlv.define_pool() without a 4th parameter (cleanup_env)
    results in failure since 4th parameter is expected
 2. The local 'get_image_info' should be replaced by the virt-test
    virttest/utils_misc/get_image_info().  Doing so changes the name
    of the 'img_info' field 'capacity' to 'vsize'. Since this field
    is already an 'int' bytes value - the code in norm_capacity() to
    "read" the bytes value is no longer necessary and a straight
    assignment is possible.
 3. Various 'actual_info' dictionary key's were mis-capitalized.