If the VIR_STRDUP(exptime,...) fails, then we will jump to cleanup,
no need to check if exptime is set which causes Coverity to issue
a complaint in the virStrToLong_ll call because there wasn't a check
for a NULL value while there was one for the reference right after
the VIR_STRDUP().
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>