list: fix exit code for --verbose and --pinned

`brew list --verbose <formulae>` lists only those kegs that
are installed and exits with 0 if all <formulae> installed.
If one or more formulae from <formulae> are not installed, the
command lists only installed versions and exits with 1.

`brew --pinned formula` exits with 1 if formula is not pinned.

Fixes #1172

Library/Homebrew/cmd/list.rb

@@ -106,7 +106,11 @@ def filtered_list
     names = if ARGV.named.empty?
       Formula.racks
     else
-      ARGV.named.map { |n| HOMEBREW_CELLAR+n }.select(&:exist?)
+      racks = ARGV.named.map { |n| HOMEBREW_CELLAR+n }
+      racks.select do |rack|
+        Homebrew.failed = true unless rack.exist?
+        rack.exist?
+      end
     end
     if ARGV.include? "--pinned"
       pinned_versions = {}