fixed gcc warnings that call returns not checked

modified:   src/collect/collect.c
modified:   src/udev/udev-node.c
modified:   src/udev/udevadm-settle.c
modified:   src/udev/udevd.c
GCC warns that the return values are not being checked for some  stdlib calls.  This patch adds checking for these calls and returns error values in keeping with the surrounding code if they fail.