build+docs: switch to python3, refresh FAQ and INSTALL documents

Refs: #5095
Change-Id: Icdc0e9463b28c07783edbe392a9bc47136947e3b
diff --git a/.jenkins.d/util.sh b/.jenkins.d/util.sh
index 8ddc4ba..8077a74 100644
--- a/.jenkins.d/util.sh
+++ b/.jenkins.d/util.sh
@@ -16,6 +16,7 @@
     set ${saved_xtrace}
     return ${ret}
 }
+export -f has
 
 sudo_preserve_env() {
     local saved_xtrace
@@ -35,3 +36,4 @@
     set ${saved_xtrace}
     sudo env "${vars[@]}" "$@"
 }
+export -f sudo_preserve_env