rpm: depend on python2, not bare python

Fedora requires packages to depend on "python2" RPM, not the unversioned
"python" name. Fortunately even though RHEL-6 ships a "python" RPM, it
has a virtual Provides for the "python2" name, so we don't need to
conditionalize this.
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

libvirt.spec.in

@@ -305,7 +305,7 @@ BuildRequires: perl-interpreter
 %else
 BuildRequires: perl
 %endif
-BuildRequires: python
+BuildRequires: python2
 %if %{with_systemd}
 BuildRequires: systemd-units
 %endif

mingw-libvirt.spec.in

@@ -61,7 +61,7 @@ BuildRequires:  pkgconfig
 # Need native version for msgfmt
 BuildRequires:  gettext
 BuildRequires:  libxslt
-BuildRequires:  python
+BuildRequires:  python2
 %if 0%{?fedora} >= 27
 BuildRequires:  perl-interpreter
 %else