apacheconf: sane sudo letsencrypt (fixes #2800)

- hardcoded
  `LETSENCRYPT=/home/travis/build/letsencrypt/letsencrypt/.tox/apacheconftest/bin/letsencrypt`
  causes Travis tests to fail if running under any other Travis user
  (from e.g. a fork)

- `sudo env "PATH=$PATH" letsencrypt` should make sure that sudo can
  find letsencrypt binary from virtualenv; realpath is not necessary

- sudo is called already from within the test script, no need to sudo
  the entire script

letsencrypt-apache/letsencrypt_apache/tests/apache-conf-files/apache-conf-test

@@ -5,9 +5,7 @@
 
 export EA=/etc/apache2/ 
 TESTDIR="`dirname $0`"
-LEROOT="`realpath \"$TESTDIR/../../../../\"`"
 cd $TESTDIR/passing
-LETSENCRYPT="${LETSENCRYPT:-$LEROOT/venv/bin/letsencrypt}"
 
 function CleanupExit() {
     echo control c, exiting tests...
@@ -61,7 +59,7 @@ trap CleanupExit INT
 for f in *.conf ; do 
     echo -n  testing "$f"...
     Setup
-    RESULT=`echo c | sudo "$LETSENCRYPT" -vvvv --debug --staging --apache --register-unsafely-without-email --agree-tos certonly -t 2>&1`
+    RESULT=`echo c | sudo env "PATH=$PATH" letsencrypt -vvvv --debug --staging --apache --register-unsafely-without-email --agree-tos certonly -t 2>&1`
     if echo $RESULT | grep -Eq \("Which names would you like"\|"mod_macro is not yet"\) ; then
         echo passed
     else