libuuid: avoid double open and leaking fd (reworked)

libuuid: avoid double open and leaking fd (reworked)

This reverts commit 6126f7a53c57485a9a29ddd772765695f23c92e6
and fixes the double open and leaking descriptor in a different way,
that is by using newly introduced function 'have_random_source()'
to check whether good random source is available while deciding
which uuid type to generate (random/time).

This is better than calling random_get_fd() twice, passing the file
descriptor down the stack and reusing it in next call to
random_get_fd().

Signed-off-by: Petr Uzel <petr.uzel@suse.cz>