Fix numerous Coverity issues in mptutil

Fix numerous Coverity issues in mptutil

Most are memory or file descriptor leaks. Three were unannotated
fallthroughs in a switch/case statement. One was an integer overflow before
widen.

Reported by:	Coverity
CID:		1007463 1007462 1007461 1007460 1007459 1007458 1007457
CID:		1006855 1006854 1006853 1006852 1006851 1006850 1006849
CID:		1006848 1006845 1006844 1006843 1006842 1006841 1006840
CID:		1006839 1006838 1006837 1006836 1006835 1006834 1006833
CID:		1006832 1006831 1006831 1006830 1006829 1008334 1008170
CID:		1008169 1008168
MFC after:	3 weeks
Sponsored by:	Spectra Logic Corp
Differential Revision:	https://reviews.freebsd.org/D11013