Improve bash quoting, and other similar best practices

This patch updates the shell scripts with some of the common best
practices, which should make them more resilient to unusual failures and
unexpected environments (in particular, directories with spaces).

Most of these were identified by shellcheck.

test/cover.sh

@@ -10,7 +10,7 @@
 # coverage_test.go), but works for now.
 
 set -e
-. $(dirname ${0})/util/lib.sh
+. "$(dirname "$0")/util/lib.sh"
 
 init
 
@@ -28,11 +28,11 @@ export COVER_DIR="$PWD/.coverage"
 # tests, which don't expect any expvars to exists besides the one registered
 # in the tests themselves.
 for pkg in $(go list ./... | grep -v -E 'chasquid/cmd/|chasquid/test'); do
-	OUT_FILE="$COVER_DIR/pkg-`echo $pkg | sed s+/+_+g`.out"
+	OUT_FILE="$COVER_DIR/pkg-${pkg//\//_}.out"
 	go test -tags coverage \
 		-covermode=count \
 		-coverprofile="$OUT_FILE" \
-		-coverpkg=./... $pkg
+		-coverpkg=./... "$pkg"
 done
 
 # Integration tests.
@@ -61,5 +61,5 @@ go run "${UTILDIR}/coverhtml/coverhtml.go" \
 echo
 echo
 echo "Coverage report can be found in:"
-echo file://$COVER_DIR/coverage.html
+echo "file://$COVER_DIR/coverage.html"