Since Go 1.7, "context" is a standard package, superceding the
"x/net/context". Since Go 1.9, the latter only provides type aliases
from the former. Therefore, it makes sense to switch to the standard
package, and the change is not disruptive in any sense.

This commit deals with a few cases where both packages happened to be
imported by the same source file. A choice between "context" and
"gocontext" was made for each file in order to minimize the patch.

Signed-off-by: Kir Kolyshkin <[email protected]>

Since Go 1.7, context is a standard package, superceding the
"x/net/context". Since Go 1.9, the latter only provides a few type
aliases from the former. Therefore, it makes sense to switch to the
standard package.

This commit was generated by the following script (with a couple of
minor fixups to remove extra changes done by goimports):

	#!/bin/bash

	if [ $# -ge 1 ]; then
		FILES=$*
	else
		FILES=$(git ls-files \*.go | grep -vF ".pb.go" | grep -v
	^vendor/)
	fi

	for f in $FILES; do
		printf .
		sed -i -e 's|"golang.org/x/net/context"$|"context"|' $f
		goimports -w $f
		awk '	/^$/ {e=1; next;}
			/[[:space:]]"context"$/ {e=0;}
			{if (e) {print ""; e=0}; print;}' < $f > $f.new && \
				mv $f.new $f
		goimports -w $f
	done
	echo

Signed-off-by: Kir Kolyshkin <[email protected]>