Bash scripts; use double brackets, fix bare variables, add quotes

These scripts explicitly use Bash, so we should be able to use
`[[` instead of `[` (which seems to be recommended).

Also added curly brackets to some bare variables, and quoted some paths.

This makes my IDE a bit more silent :-)

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

hack/validate/dco

@@ -21,13 +21,13 @@ check_dco() {
 	grep -qE "$dcoRegex"
 }
 
-if [ $adds -eq 0 -a $dels -eq 0 ]; then
+if [[ ${adds} -eq 0 && ${dels} -eq 0 ]]; then
 	echo '0 adds, 0 deletions; nothing to validate! :)'
 else
 	commits=( $(validate_log --format='format:%H%n') )
 	badCommits=()
 	for commit in "${commits[@]}"; do
-		if [ -z "$(git log -1 --format='format:' --name-status "$commit")" ]; then
+		if [[ -z "$(git log -1 --format='format:' --name-status "$commit")" ]]; then
 			# no content (ie, Merge commit, etc)
 			continue
 		fi
@@ -35,7 +35,7 @@ else
 			badCommits+=( "$commit" )
 		fi
 	done
-	if [ ${#badCommits[@]} -eq 0 ]; then
+	if [[ ${#badCommits[@]} -eq 0 ]]; then
 		echo "Congratulations!  All commits are properly signed with the DCO!"
 	else
 		{