Double quote some statements for zsh compatibility

Two eval commands did not enclose their arguments in double quotes, and
this broke compatibility on zsh - preventing lunch from running to
completion. This CL adds the double quotes and fixes the issue.

Change-Id: I5ed884b455e2e61182f6c29fb807ed92372af039
diff --git a/envsetup.sh b/envsetup.sh
index 101ef13..3393b75 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -89,7 +89,7 @@
 {
     if [ "$BUILD_VAR_CACHE_READY" = "true" ]
     then
-        eval echo \"\${abs_var_cache_$1}\"
+        eval "echo \"\${abs_var_cache_$1}\""
     return
     fi
 
@@ -107,7 +107,7 @@
 {
     if [ "$BUILD_VAR_CACHE_READY" = "true" ]
     then
-        eval echo \"\${var_cache_$1}\"
+        eval "echo \"\${var_cache_$1}\""
     return
     fi