Python3 support in build scripts

Python 2.7 is soon loosing support and as a result we gradually abandoned it in the 2nd half of 2019.  We have certainly not been early adopters!

Now, building Qpid from source, I find that it still relies on this old version.  It does not even notice though, which is not very handy in a time that people are migrating:

{{-- Found PythonInterp: /usr/bin/python (found suitable version "3.7.3", minimum required is "2.7") }}
{{-- Found PythonInterp: /usr/bin/python (found version "3.7.3") }}
{{ File "<string>", line 1}}
{{ from distutils.sysconfig import get_python_lib; print get_python_lib(False, prefix='/usr/local').replace('
', '/')}}
{{ ^}}
SyntaxError: invalid syntax
CMake Error at managementgen/CMakeLists.txt:34 (install):
{{ install DIRECTORY given no DESTINATION!}}

Python3 bails out with an error, about the lack of parenthesis, but CMake concludes its own things.  Looking silly.  It does continue to one more similar error:

-- Regenerating Qpid Management Framework sources
{{ File "/usr/local/src/qpid-cpp-broker.git/managementgen/qmf-gen", line 64}}
{{ print "no input files"}}
{{ ^}}
SyntaxError: Missing parentheses in call to 'print'. Did you mean print("no input files")?
CMake Error at src/CMakeLists.txt:141 (include):
{{ include could not find load file:}}/usr/local/src/qpid-cpp-broker.git/build/src/managementgen.cmake
CMake Error at /usr/share/cmake-3.13/Modules/FindBoost.cmake:2100 (message):
{{ Unable to find the requested Boost libraries.}}Unable to find the Boost header files. Please set BOOST_ROOT to the root
{{ directory containing Boost or BOOST_INCLUDEDIR to the directory containing}}
{{ Boost's headers.}}
Call Stack (most recent call first):
{{ src/CMakeLists.txt:194 (find_package)}}
CMake Error at /usr/share/cmake-3.13/Modules/FindBoost.cmake:2100 (message):
{{ Unable to find the requested Boost libraries.}}Unable to find the Boost header files. Please set BOOST_ROOT to the root
{{ directory containing Boost or BOOST_INCLUDEDIR to the directory containing}}
{{ Boost's headers.}}
Call Stack (most recent call first):
{{ src/CMakeLists.txt:208 (find_package)}}
CMake Error at src/CMakeLists.txt:210 (message):
{{ Required Boost C++ libraries not found. Please install or try setting}}
{{ BOOST_ROOT}}
-- Configuring incomplete, errors occurred!

Again, the parenthesis of print.  And again, CMake concludes its own things, presumably from the exit value.

I don't believe I am being a Python3 pusher at this time, not anymore; last year it has been anounced that Python2.7 would be gone at the start of 2020.  (I checked again and found it is now set at April 2020 but still very soon.)

Please update Qpid accordingly, so people relying on Python3 for security/updates have a way to continue using/building Qpid?  By now, everyone should at least be able to run Python3, or else that is a fair upgrade expectation, as it will soon be the only real Python left.

Thanks!

 -Rick