Install python scripts properly in nightly docker image

The nightly image doesn't contain scripts from lalinference/python, e.g.

root@b1aed652a1f9:/# lalinference_pipe
/usr/bin/python: can't open file '/builds/lscsoft/lalsuite/opt/lalsuite/libexec/lalinference/lalinference_pipe.py': [Errno 2] No such file or directory

None of the pybin_scripts listed in lalinference/python/Makefile.am are copied into the installation directory properly.

@adam-mercer suggested that a similar issue has been fixed in the pkgconfig files already.