Update RPM .spec file to use Python 2 on EL7. HTCONDOR-549

Remove Python 3 requirements. Rewrite .py shebang lines to use python2.

rpm/blahp.spec

@@ -4,7 +4,9 @@
 %define bl_libexecdir %{_libexecdir}/%{name}
 
 # Force brp-python-bytecompile to use Python 3
+%if ! 0%{?rhel} == 7
 %global __python /usr/bin/python3
+%endif
 
 Name:		blahp
 Version:	2.1.0
@@ -31,7 +33,9 @@ BuildRequires:  globus-gsi-proxy-core-devel
 BuildRequires:  globus-gsi-cert-utils-devel
 BuildRequires:  docbook-style-xsl, libxslt
 
+%if ! 0%{?rhel} == 7
 Requires:       python3
+%endif
 
 %description
 %{summary}
@@ -40,6 +44,10 @@ Requires:       python3
 %setup
 
 %build
+%if 0%{?rhel} == 7
+# Don't rely on Python 3 on EL7 (not installed by default)
+sed -i 's;/usr/bin/python3;/usr/bin/python2;' src/scripts/*status.py
+%endif
 ./bootstrap
 export CPPFLAGS="-I/usr/include/classad -std=c++11 -fcommon"
 export LDFLAGS="-lclassad -lglobus_gsi_credential -lglobus_common -lglobus_gsi_proxy_core"