rpm: update all rpm files for using python3.

This includes:
- tools/rpm-setup.sh
- packaging/rpm/wireshark.spec.in

Fixes: v2.9.0rc0-2460-ge9f7bb5127 ("Require Python 3, drop Python 2 support")
Change-Id: I9fb92be936dec5fdb819a54e132e64521fa95bbb
Reviewed-on: https://code.wireshark.org/review/30543
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Jeff Morriss <jeff.morriss.ws@gmail.com>
Reviewed-by: Dario Lombardo <lomato@gmail.com>

packaging/rpm/wireshark.spec.in

@@ -51,11 +51,12 @@ BuildRoot:	/tmp/%{name}-%{version}-%{release}-root-%(%{__id_u} -n)
 
 %if 0%{?rhel}
 BuildRequires:	cmake3 >= 3.5
+BuildRequires:  python34
 %else
 BuildRequires:	cmake >= 3.5
+BuildRequires:  python3
 %endif
 BuildRequires:	gcc
-BuildRequires:	python3
 BuildRequires:	perl
 BuildRequires:	flex
 BuildRequires:	bison

tools/rpm-setup.sh

@@ -42,7 +42,6 @@ BASIC_LIST="gcc \
 	gcc-c++ \
 	flex \
 	bison \
-	python \
 	perl \
 	lua-devel \
 	lua \
@@ -111,6 +110,11 @@ add_package() {
 	eval "${list}=\"\${${list}} \${pkgname}\""
 }
 
+# python3: OpenSUSE 43.3, Fedora 26
+# python34: Centos 7
+add_package BASIC_LIST python3 || add_package BASIC_LIST python34 ||
+echo "python3 is unavailable" >&2
+
 add_package BASIC_LIST cmake3 || add_package BASIC_LIST cmake ||
 echo "cmake is unavailable" >&2