Pull request: home: rm var shadowing, vol. 4

Closes #2803.

Squashed commit of the following:

commit cb36cc8811160bb39a32fb8eddf962d0ebe9035a
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Mar 12 14:21:46 2021 +0300

    home: imp more

commit 9ea7ccec8bb293881cf724d7ad57e6744243d8b9
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Mar 12 13:58:10 2021 +0300

    all: imp naming, refactor http srv shutdown

commit f29221007c16fd3e7230bf2c1ac37b365f3e29aa
Merge: 2247c05b bfbf73f3
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Mar 12 13:35:17 2021 +0300

    Merge branch 'master' into 2803-shadow-4

commit 2247c05b5521346aaf362d81ccdd64fee31f1e6d
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Jan 29 20:53:21 2021 +0300

    home: rm var shadowing, vol. 4

internal/home/options.go

@@ -296,15 +296,14 @@ func parse(exec string, ss []string) (o options, f effect, err error) {
 					}
 					if eff != nil {
 						prevf := f
-						f = func() error {
-							var err error
+						f = func() (ferr error) {
 							if prevf != nil {
-								err = prevf()
+								ferr = prevf()
 							}
-							if err == nil {
-								err = eff()
+							if ferr == nil {
+								ferr = eff()
 							}
-							return err
+							return ferr
 						}
 					}
 				}