MFC r294347

Fix usr.bin.truncate.truncate_test.bad_truncate with ZFS /tmp.

The bad_truncate test sets the uimmutable flag to produce an error in
truncate, but that flag isn't supported by ZFS. If /tmp is on a ZFS
filesystem, the test will fail. Change it to use readonly permissions and
an unpriveleged user instead.

MFC r267265: truncate: Detect integer overflow, fix relative sizes, add tests.

The change to expand_number (r204654) broke detection of too large sizes and
relative sizes ('+'/'-').

Also add some tests.

The usr.bin/truncate/Makefile is slightly different in the MFC because
src.opts.mk does not exist in stable/10.

PR: 190735
Submitted by: Kirk Russell

truncate: Detect integer overflow, fix relative sizes, add tests.

The change to expand_number (r204654) broke detection of too large sizes and
relative sizes ('+'/'-').

Also add some tests.

PR: 190735
Submitted by: Kirk Russell
MFC after: 1 week