C library: Fix lsm_local_disk_list() to skip non-exist disks.
C library: Fix lsm_local_disk_list() to skip non-exist disks.

Problem:
    When running in fakeroot, lsm_local_disk_list() might indicate the
    existence of '/dev/sda' while lsm_ident_led_on() fail with
    NOT_FOUND_DISK error.

Root cause:
    The fakeroot might only have /sys mounted while /dev/ is not.

Fix:
    Make sure the file '/dev/sdX' exists before add it to return list.

Signed-off-by: Gris Ge <e24f3acbe39bf94f92e8af3c48f8852106ad5ad7@redhat.com>

joehandzik/libstoragemgmt,libstorage/libstoragemgmt,tasleson/libstoragemgmt,joehandzik/libstoragemgmt,jumitche/libstoragemgmt,cathay4t/libstoragemgmt,cathay4t/libstoragemgmt,joehandzik/libstoragemgmt,jumitche/libstoragemgmt,libstorage/libstoragemgmt,libstorage/libstoragemgmt,tasleson/libstoragemgmt,cathay4t/libstoragemgmt,jumitche/libstoragemgmt,cathay4t/libstoragemgmt,cathay4t/libstoragemgmt,tasleson/libstoragemgmt,libstorage/libstoragemgmt,tasleson/libstoragemgmt,jumitche/libstoragemgmt,jumitche/libstoragemgmt,joehandzik/libstoragemgmt,libstorage/libstoragemgmt,tasleson/libstoragemgmt