specfile: fix logic for detecting if Python2 is supported

It's now less obfuscated.
Python2 was conditionally enabled only if building for an old
RHEL or old SLES but the version tests was not correct.

Thanks to Matt Ezell from  Oak Ridge.

Fixes #445.
Signed-off-by: Egbert Eich <eich@suse.com>

clustershell.spec.in

@@ -21,7 +21,7 @@
 %{!?__python3: %global __python3 python3}
 %{!?python3_shortver: %global python3_shortver %(%{__python3} -c 'import sys; print(str(sys.version_info.major) + "." + str(sys.version_info.minor))')}
 
-%if ! 0%{?rhel} >= 8 && ! 0%{?suse_version} > 1550
+%if 0%{?rhel} < 8 &&  0%{?suse_version} <= 1500
 %define py2 1
 %endif