build: prefer mkostemp for multi-thread safety

build: prefer mkostemp for multi-thread safety

https://bugzilla.redhat.com/show_bug.cgi?id=871756

Commit cd1e8d1 assumed that systems new enough to have journald
also have mkostemp; but this is not true for uclibc.

For that matter, use of mkstemp[s] is unsafe in a multi-threaded
program.  We should prefer mkostemp[s] in the first place.

* bootstrap.conf (gnulib_modules): Add mkostemp, mkostemps; drop
mkstemp and mkstemps.
* cfg.mk (sc_prohibit_mkstemp): New syntax check.
* tools/virsh.c (vshEditWriteToTempFile): Adjust caller.
* src/qemu/qemu_driver.c (qemuDomainScreenshot)
(qemudDomainMemoryPeek): Likewise.
* src/secret/secret_driver.c (replaceFile): Likewise.
* src/vbox/vbox_tmpl.c (vboxDomainScreenshot): Likewise.