Fix Coverity CIDs in the sys/kern/sysv_test tests

CID 979810: strcpy => strlcpy
CID 1193367: don't leak a file descriptor
CID 1299856: Check the return value of read(2)

Reported by: Coverity
Coverity CID: 978910 1193367 1299856
MFC after: 3 weeks
X-MFC-With: 328896
Sponsored by: Spectra Logic Corp