host/cli: Work around segfault in TUF update
host/cli: Work around segfault in TUF update

Add a temporary workaround that avoids an apparent intermittent
segfault in the buffer pool implementation of
ioutil.Discard.ReadFrom observed on EC2 with Go 1.4.3.

This patch should be removed on Go 1.5 to test whether the problem
still exists.

Closes #2211

Signed-off-by: Jonathan Rudenberg <3692bfa45759a67d83aedf0045f6cb635a966abf@titanous.com>

lmars/flynn,lmars/flynn,benbjohnson/flynn,benbjohnson/flynn,flynn/flynn,flynn/flynn,philiplb/flynn,philiplb/flynn,philiplb/flynn,lmars/flynn,flynn/flynn,benbjohnson/flynn,lmars/flynn,flynn/flynn,philiplb/flynn,benbjohnson/flynn,lmars/flynn,benbjohnson/flynn,philiplb/flynn,flynn/flynn,benbjohnson/flynn