elements: Drop executable bits from environment files

Files in $element/environment.d are meant to be sourced, so drop
the executable bit. Moreover, drop the executable bit from a couple
of other scripts that are either meant to be sourced or simply because
they are configuration files.

Change-Id: I7f724dd9d409f4a835a136f12f48a84aa9acc41e

bin/dib-lint

@@ -156,11 +156,15 @@ for i in $(find elements -type f   \
         fi
     fi
 
-    # check that environment files don't "set -x"
+    # check that environment files don't "set -x" and they have no executable
+    # bits set
     if [[ "$i" =~ (environment.d) ]]; then
         if grep -q "set -x" $i; then
             error "Environment file $i should not set tracing"
         fi
+        if [[ -x $i ]]; then
+            error "Environment file $i should not be marked as executable"
+        fi
     fi
 
     # check that sudo calls in phases run outside the chroot look