treewide: stop run from discarding error messages

In most cases where this function is used, suppressing only the standard
output is more appropriate. Culling diagnostic output hides error
messages and makes debugging more difficult and confusing.

`$DRY_RUN_NULL`, which the `--silence` flag replaced, was used both for
suppressing standard output on its own, and for doing so along with
diagnostic output; however, when the `run` function was added this
distinction was lost, and both outputs would be discarded.

This reintroduces the needed functionality, and changes usages of
`--silence` to `--quiet` where previously only standard output was
suppressed, or where this should have probably been the case anyway.

Change-Id: Ifb1b52a1d1eea0117261c782d686ad7c71b43162

modules/lib-bash/activation-init.sh

@@ -115,7 +115,7 @@ function nixProfileRemove() {
         nixProfileList "$1" | xargs -rt $DRY_RUN_CMD nix profile remove $VERBOSE_ARG
     else
         if nix-env -q | grep -q "^$1$"; then
-            run --silence nix-env -e "$1"
+            run --quiet nix-env -e "$1"
         fi
     fi
 }