ply-keyfile: Change ply_key_file_get_long () into ply_key_file_get_ulong ()

ply-keyfile: Change ply_key_file_get_long () into ply_key_file_get_ulong ()

Change ply_key_file_get_long () into ply_key_file_get_ulong () and add
error checking.

All callers of ply_key_file_get_long () expect a positive / unsigned number.
Rename it to ply_key_file_get_ulong ().

Also add error checkig for non valid numbers and return the default value
for these instead of 0.

Note this also fixes the return value of ply_key_file_get_long () being
a double (this is now changed to an unsigned long).

Signed-off-by: Hans de Goede <hdegoede@redhat.com>