Add -debug-on-fail option to "xe" and other minor improvements
Add -debug-on-fail option to "xe" and other minor improvements

Unlike -debug, -debug-on-fail will only output debug information and connection diagnosis when the exit code is not 0.

Signed-off-by: Zheng Li <34c6fceca75e456f25e7e99531e2425c6c1de443@zheng.li>

johnelse/xcp-rrdd,koushikcgit/xcp-networkd,koushikcgit/xcp-rrdd,koushikcgit/xcp-networkd,djs55/xcp-rrdd,robhoes/squeezed,sharady/xcp-networkd,djs55/xcp-rrdd,koushikcgit/xcp-rrdd,koushikcgit/xcp-rrdd,djs55/xcp-networkd,simonjbeaumont/xcp-rrdd,sharady/xcp-networkd,simonjbeaumont/xcp-rrdd,djs55/squeezed,johnelse/xcp-rrdd,djs55/xcp-networkd